Blocking calls from strangers: 9 ways to block spam and unwanted calls.

Nothing is more annoying than being constantly disturbed while resting or working by strange calls, offers to buy insurance, renew your car warranty, or other unsolicited services. If you're tired of spam calls and advertising messages, it's time to take action.

This article will guide you on how to block unknown calls , spam numbers, and unwanted numbers on your phone simply and effectively — helping you stay safe, protect your personal information , and avoid falling into scams .

However, it's important to remember that some scammers can still find ways to make calls , so completely blocking them is very difficult. Even so, by applying the following methods correctly, you can reduce nuisance calls by up to 90% each day.

How to effectively block spam calls and unwanted numbers.

If you frequently receive unsolicited calls from unknown numbers advertising, selling, or offering services, here are some simple and practical ways to minimize these annoying calls:

• Sign up for the "Do Not Receive Marketing Calls" list :
  In the U.S., you can visit the FTC (Federal Trade Commission) website or call 1-888-382-1222 to add your phone number to the Do Not Call list. Once registered, legitimate marketing entities will not be allowed to contact you.

• Block advertising phone numbers directly :
  When you receive a harassing call, immediately block that number in your phone's "Call History." This will prevent that number from calling again in the future.

• Contact your mobile carrier for assistance in blocking anonymous calls .
  Many mobile service providers now offer services to block calls from unknown or anonymous numbers . Call customer service and request to activate this feature for better protection.

• Additional note :
  Even if you've followed all the steps above, some scam calls can still slip through the system . Therefore, never provide personal information, OTP codes, or banking data over the phone unless you are absolutely certain of the caller's identity.

Method 1: Sign up for the "Do Not Receive Spam Calls" list to block unwanted numbers.

One of the most effective ways to reduce spam calls is to add your phone number to the Do Not Call Registry managed by the U.S. Federal Trade Commission (FTC) . Here are the specific instructions and things you need to know:

• How to register:

  • Visit the official website: www.donotcall.gov.

  • Or call 1-888-382-1222 .

  • Please provide your name and phone number to verify your information.

  • This can be applied to both mobile and landline numbers.

• Benefits after signing up:

  • Legitimate companies are not permitted to make advertising calls or offer services to you.

  • Making marketing calls to registered phone numbers is illegal .

• Cases where you can still call:

  • Political organizations, charities, and non-profit organizations still have the right to contact them.

  • This list is only for filtering out commercial and sales calls .

• Validity period:

  • It may take up to 31 days for the system to update and for advertising calls to stop completely.

  • If you still receive a few calls in the beginning, don't worry too much — that's normal.

• Important note:

  • Scammers don't comply with this rule , so you might still occasionally receive suspicious calls.

  • If you see an unfamiliar number or suspicious content, do not share personal information , especially OTP codes, account numbers, or bank information .

Method 2: Report phone numbers that violate advertising regulations.

After you've signed up to the "Do Not Call" list , any marketing calls from commercial companies will be considered illegal . If you are still being harassed, you can report it directly for action .

• How to generate the report:

  • Visit the official website: www.donotcall.gov.

  • Select the option “Report it to the FTC” .

  • Enter the necessary information:

    • This is the phone number that called you.

    • The time, content, or topic of the call.

  • Submit the information and wait for the authorities to verify and process it.

• Benefits of reporting:

  • When reported, legitimate companies will receive a warning or administrative fine , which helps reduce the risk of repeat offenses.

  • By proactively reporting your number, you may cause marketing agencies to permanently stop contacting you.

• A factual note:

  • Some scammers use the tactic of "phone number spoofing" —that is, changing the displayed number for incoming calls each time.

  • If you receive multiple calls from the same area or similar area code , reporting them may not completely block them , but it will still help the FTC collect data for investigation .

• Further suggestions:

  • Do not respond or press any keys during a suspicious call.

  • Block the number that just called to prevent it from happening again.

  • Use a spam call blocking app (such as Truecaller, Hiya, or an app provided by your carrier).

Option 3: Ask the operator to stop making promotional calls to you.

In some cases, you might accidentally answer a call while waiting for an important one — and the person on the other end is a sales or marketing call . Don't get upset or argue; just handle it quickly, decisively, and properly :

• Ways to say "I'm going to stop taking a call":

  • Stay calm and speak clearly:
    "Please add my number to your do-not-receive-telephone list."

  • Then hang up immediately , without continuing the conversation.

  • This statement has legal effect on legitimate companies — they must stop contacting you if you have requested it.

• Why you shouldn't argue or yell:

  • Call center operators are trained to keep calls going for as long as possible .

  • The longer the conversation lasts, the easier it is to be "held captive" and persuaded to come back to listen or make a purchase.

  • Maintaining a polite but firm attitude is the most effective approach.

• When does this method work?

  • Only effective with legitimate companies or call centers.

  • In many states (in the US) and also in Vietnam, continuing to call after being asked to stop is a violation of regulations on telemarketing .

• If it's a scam call:

  • These individuals often disregard the law , so requests to stop calling will be ineffective .

  • In that case, block the number immediately and report it to the regulatory authority or your network provider for assistance.

Method 4: Manually block advertising phone numbers after receiving calls.

If you frequently receive calls from the same company or landline number, manually blocking them will help you completely prevent repeat calls . However, this method is not effective against spoofed numbers —numbers that change with each call.

• How to block ads on iPhone:

  • Open the Recent Calls list .

  • Tap the "i" icon next to the number you just called.

  • Scroll to the bottom of the page and select “Block this caller” .

  • That number will be completely blocked; they won't be able to call or text you.

• How to block on Android phones:

  • Open the Phone app, then go to Recent calls .

  • Select the number you want to block, tap the “i” icon or the three-dot menu (…) .

  • Choose either "Block" or "Reject calls from this number" depending on your phone model.

  • Alternatively, you can go to Settings > Calls > Call blocking/Call rejection to manually add numbers.

• Note:

  • This method works with legitimate advertising companies , which often call back from the same number.

  • With fraudulent or scam calls , they often use a different number each time , so manually blocking only helps to reduce the frequency of the calls to some extent .

  • To increase effectiveness, you can combine this with a spam call blocking app such as Truecaller, Hiya, or a blocking tool provided by Vietnamese network operators (e.g., Viettel, VinaPhone, MobiFone).

Method 5: Enable anonymous call blocking to avoid being disturbed.

One of the biggest sources of annoyance is "anonymous" calls, or calls where the caller's identity is not displayed . You can proactively enable anonymous call blocking to minimize this.

• Contact your carrier to enable anonymous call blocking:

  • Call the customer service hotline of your mobile network provider (Viettel, VinaPhone, MobiFone, etc.).

  • Ask if they offer anonymous call blocking services .

  • Many carriers can activate this feature remotely , or guide you through the process directly on your phone.

  • Some systems in the US can be quickly activated using the code *77 , but in Vietnam, you need to verify with your network provider because this code may have other uses (even contacting emergency services).

• Service fee:

  • Some carriers may charge a small monthly fee for anonymous call blocking services.

  • However, if you frequently receive calls from anonymous numbers , this fee is well worth the investment to ensure your privacy and security.

• Enable blocking of hidden numbers directly on your phone:

  • Many current iPhone and Android devices have a "Block calls without showing the number" feature.

  • Go to Settings > Phone and look for the option “Silence Unknown Callers” (iPhone) or “Block anonymous calls” (Android, depending on the model).

• Limitations of the feature:

  • This feature only blocks numbers that display as “Anonymous”, “Unknown”, or “Private Number” .

  • Specific numbers or legitimate company numbers may still call — but you can manually block each number after receiving a call.

Method 6: Ask your carrier about scam call blocking services to better protect yourself.

If you are frequently bothered by unwanted calls from unknown numbers, advertising numbers, or scam calls, take advantage of your carrier's own call blocking service . This is the most effective, safe, and least time-consuming method because the carrier's system can automatically filter and block calls before they reach your phone.

• Benefits of a scam call blocking service:

  • Mobile network operators can monitor and analyze call traffic to identify suspicious behavior.

  • The system will automatically block or warn you when you receive a call from spam, fake, or fraudulent sources .

  • You don't need to manually block each number — everything is handled at the system level .

• Here are some examples of services that block international calls:

  • AT&T: The free “AT&T Call Protect” app helps block and alert you to suspicious numbers.

  • Verizon: The "Caller Filter" service costs approximately $2.99 ​​per month .

  • T-Mobile: Call #622 to enable Scam Filtering; charges may apply depending on your plan.

  • Sprint offers a “Premier Caller ID” service for $2.99/month , which displays and alerts you to suspicious calls.

• In Vietnam:

  • Mobile network operators such as Viettel, VinaPhone, and MobiFone all offer free or low-cost services to block spam and scam calls .

  • You can:

    • Send a text message or call customer service to activate your account.

    • Use your mobile carrier's app, such as My Viettel, My MobiFone, or My VNPT , to enable the "Block spam/scam calls" feature.

• When should you use this service?

  • If you are being harassed frequently , or your phone number has been leaked .

  • If you don't have time to manually block each number , this is the most time-saving and cost-effective solution .

Method 7: Download an app to block spam and scam calls for more effective phone protection.

If you want to proactively control and filter out spam, advertising, or scam calls , using a dedicated call blocking app is the smartest and most convenient option. These apps automatically identify, warn, or block suspicious numbers , helping you avoid daily nuisances.

• Popular call blocking apps around the world:

  • RoboKiller: Distinguished by its ability to detect and block spoofed numbers , especially useful if you frequently receive calls from numbers with the same area code .

  • Hiya: An easy-to-use app that can display caller ID and warn you of spam or scam calls in real time.

  • Nomorobo: Focuses on filtering automated calls (robocalls) and blocking messages containing suspicious links .

• Key features of these applications:

  • Automatically block or alert you when you receive a call that you suspect is spam or a scam.

  • Identify unknown numbers before you answer, helping you decide whether or not to respond.

  • Block spam messages , especially those containing malicious links leading to phishing websites.

  • Customize your block list to suit your personal needs — for example, only allow contacts from your address book.

• Regarding costs:

  • All of these apps offer free trial versions and free basic plans with limited features.

  • To use all the advanced features, you need to pay a monthly fee , usually only a few tens of thousands of Vietnamese dong .

• Suggestions for users in Vietnam:

  • You can also check out other popular call blocking apps such as Truecaller , CallApp , or Smart Call Blocker .

  • In addition, many Vietnamese mobile network operators have also integrated a spam call blocking feature into their subscriber management applications (My Viettel, My VNPT, My MobiFone).

Method 8: Turn on "Do Not Disturb" mode to block all calls from numbers not in your contacts.

If you've tried many methods but are still constantly bothered by spam calls, advertisements, or scams , then "Do Not Disturb" mode is the most powerful and thorough solution . When this mode is enabled, all calls not in your contacts will be blocked or sent directly to voicemail , giving you complete peace and quiet.

• How to enable "Do Not Disturb" mode on Android:

  • Swipe down from the top of the screen to open the Control Center .

  • Click the “Do Not Disturb” icon for quick activation.

  • To customize, press and hold the icon , then select "Allow exceptions" .

  • Here, you can choose to only allow calls from your contacts, family members, or favorite numbers .

• How to turn it on on iPhone:

  • Go to Settings → select “Do Not Disturb” .

  • In the "Allow Calls From" section, select "Contacts Only" or "Favorites" .

  • You can also open the Control Center and tap the moon icon to quickly toggle this mode on or off.

• Advantage:

  • Block all unknown numbers, numbers with unclear identities, advertising numbers, and scam numbers.

  • Maintain your privacy , especially when working, resting, or attending important meetings.

• Disadvantages:

  • If you frequently receive calls from clients, partners, or new contacts , they will be unable to reach you when this mode is enabled.

  • Therefore, it should only be turned on temporarily , or set to automatically activate at specific times (for example, from 10 PM to 7 AM).

Method 9: Hang up immediately when you receive an automated call (robocall) to avoid being scammed.

Automated calls (robocalls) are often a ploy by shady companies or scammers . Their goal is to verify your real phone number or trick you into providing personal information . So, don't interact, don't press any keys — just hang up immediately .

• Absolutely do not follow the instructions in the automated menu:

  • Many robocalls will say: "Press 1 to unsubscribe" or "Press 2 to stop receiving calls."

  • Don't trust it and don't click! This is a scam to verify your active phone number , allowing fraudsters to sell your information to third parties .

  • As a result, you'll receive more spam calls instead of fewer.

• Why you should hang up immediately:

  • Legitimate companies usually have real people making calls, rather than using mass automated systems .

  • If it's a scam call , answering or responding will add your number to the "potential caller" list .

  • Hanging up immediately helps to sever contact before they collect more personal information .

• If you want to legally stop receiving calls:

  • You can request a call directly when a real person is speaking with you , or register on the "Do Not Call Registry" as instructed above.

  • However, this does not apply to robocalls or scam calls — as they are not in compliance with the law .

Important tips to avoid phone scams and protect your personal number.

When it comes to spam and unsolicited calls, besides blocking numbers or subscribing to "Do Not Call" lists, you need to understand the tricks scammers often use to avoid falling into their traps. Below are some practical tips to help you stay completely safe when receiving calls from unknown numbers.

• If you change your phone number:

  • Please re-register your new number in the “Do Not Call Registry” (website donotcall.gov).

  • This list doesn't update automatically , so unless you re-register, you may still receive harassing calls.

• Be wary of calls that begin with "Can you hear me?"

  • This is a voice recording scam : fraudsters will edit and splice your voice to make it appear that you have agreed to register for a service or pay a fee .

  • When you hear this type of question, hang up immediately — don't say "yes," "okay," or any other response.

• Never share personal information over the phone:

  • Do not provide your ID card/citizen identification card, account number, OTP code, bank card information, or phone verification code .

  • If you're not 100% sure of the caller's identity , it's best to say nothing and hang up immediately .

• Understanding the scope of protection offered by the "Do Not Call" list:

  • This regulation applies only to legally operating marketing companies within the United States .

  • Calls from overseas numbers can still be made, so you need to manually block them or use a call filtering app .

• Beware of dubious "vehicle warranties" or services:

  • Calls offering extended vehicle warranties or special service packages are mostly scams or sales of substandard products .

  • Even when they come from legitimate companies, these “warranty” packages are often useless, costly, and unnecessary .

• Warning signs of a scam call:

  • The caller urges you to transfer money, confirm personal information, or read out an OTP code .

  • They identified themselves as bank employees, IRS agents, police officers, court officials, etc. — but in reality, these agencies never call to demand money .

  • The IRS (US Internal Revenue Service) or similar agencies always send official letters by mail ; they never request payment over the phone.

References

1. https://www.consumer.ftc.gov/articles/0108-national-do-not-call-registry
2. https://www.consumeraffairs.com/news/how-to-stop-telemarketers-from-calling-your-cell-phone-041515.html
3. https://www.wcnc.com/article/life/former-telemarketer-shares-secrets-to-stopping-the-constant-calls/275-9013eaf1-172b-43c0-b1f2-14a580129b03
4. https://www.michigan.gov/consumerprotection/Protect-Yourself/consumer-alerts/id-theft-telemarketing/do-not-call-list
5. https://www.foxnews.com/tech/top-iphone-android-apps-for-blocking-robocalls
6. https://www.usatoday.com/story/tech/columnist/komando/2019/02/07/no-more-robocalls-how-block-unwanted-calls-iphone-android/2778059002/
7. https://www.theverge.com/21327304/spam-calls-how-to-stop-block-robocalls-robots-scam-iphone-android
8. https://www.businessinsider.com/do-not-disturb-android
9. https://support.apple.com/en-us/HT204321
10. https://www.fcc.gov/consumers/guides/stop-unwanted-robocalls-and-texts
11. https://abcnews.go.com/Business/fcc-warns-consumers-phone-scam/story?id=46405703
12. https://www.irs.gov/newsroom/how-to-know-its-really-the-irs-calling-or-knocking-on-your-door

Translated by: Lesley Collins Tran .