The fastest way to block unknown numbers
Most phones have a built-in setting that silences calls from numbers not in your contacts. On iPhone, go to Settings > Phone > Silence Unknown Callers, then toggle it on. On Android, open the Phone app, tap the three dots in the top right, select Settings > Caller ID and spam, then turn on "Filter unknown calls." These settings send unknown calls straight to voicemail without ringing your phone.
This approach stops the interruption when ready and requires no setup beyond flipping a switch. The trade-off is that legitimate callers — your doctor's office, a delivery driver, a job recruiter — will also go to voicemail. You'll need to check your voicemail regularly and call back numbers you recognize.
If you want to see who called but not be interrupted, both iPhone and Android show missed calls in your phone's call log. You can then decide whether to call back.
Key Takeaways
- iPhone's "Silence Unknown Callers" and Android's "Filter unknown calls" send unrecognized numbers straight to voicemail without ringing your phone.
- Spam-blocking apps like Nomorobo, RoboKiller, and Whoscall use databases of known spam numbers to filter calls before they reach you, though some require a paid subscription.
- You can manually block specific numbers through your phone's built-in block list, which prevents those callers from reaching you at all.
- Carrier-level blocking through AT&T Call Protect, Verizon Call Filter, or T-Mobile Scam Shield stops spam before it hits your phone, though features vary by plan.
- Combining multiple layers — carrier blocking plus your phone's unknown caller filter — catches more spam than any single method alone.
Using spam-blocking apps for more control
Apps like Nomorobo, RoboKiller, and Whoscall maintain databases of known spam and scam numbers. When a call comes in, the app checks the number against its list and either blocks it or lets it through. These apps typically show you a warning label ("Spam Risk" or "Scam Likely") before you answer, so you can decide in the moment.
Nomorobo works on both iPhone and Android and uses a shared blocklist from the FTC and other sources. RoboKiller uses artificial intelligence to identify patterns of spam calls and can even answer calls with a bot that wastes the scammer's time. Whoscall identifies callers by looking up the number in its database and showing you who is calling before you pick up.
Most of these apps are free with limited features, or charge $2 to $5 per month for full protection. The catch is that no app catches everything — new spam numbers appear constantly, and scammers rotate their numbers frequently. An app is most useful as a second layer of defense, not as your only protection.
Blocking specific numbers manually
If the same number keeps calling you, block it directly through your phone's native block list. On iPhone, open the recent call, tap the "i" icon, scroll down, and select "Block this Caller." On Android, open the Phone app, find the number in your call history, press and hold it, then tap "Block number."
Once blocked, that number cannot call or text you — the call fails on their end, and you see no notification. Blocked callers can still leave voicemail, though you won't be notified. You can unblock a number anytime by going back to your block list in Settings.
This method works well for persistent callers you recognize, but it does not help with new spam numbers. You would have to block each one individually as it calls, which becomes tedious if you receive many spam calls per day.
Using your phone carrier's spam-blocking service
Your phone company offers spam filtering as part of your plan or as an add-on. AT&T Call Protect, Verizon Call Filter, and T-Mobile Scam Shield all filter calls at the network level before they reach your phone. This means spam is stopped before it even rings, rather than being filtered on your device.
AT&T Call Protect is free for most customers and labels suspected spam calls with a warning. Verizon Call Filter is also free on most plans and blocks high-confidence spam automatically. T-Mobile Scam Shield is included with most T-Mobile plans and filters calls based on known scam patterns.
The advantage of carrier-level filtering is that it works across all your devices and does not drain your phone's battery the way an app might. The disadvantage is that you have less control over what gets blocked — the carrier decides based on its own database, and you cannot easily customize the rules.
Combining methods for better protection
No single method catches all spam. Scammers use spoofed numbers, rotate their caller IDs, and find new ways around filters constantly. The most effective approach is to layer your defenses: turn on your phone's built-in unknown caller filter, enable your carrier's spam service, and optionally add a third-party app if you still receive many unwanted calls.
Start with your phone's native settings and your carrier's service, since both are free and require no extra app. If spam calls still get through, add an app like Nomorobo or Whoscall. Monitor your voicemail for a week or two to make sure legitimate callers are not being blocked — if they are, adjust your settings to allow calls from specific numbers or disable the unknown caller filter temporarily.
Keep in mind that blocking unknown callers means you will miss calls from people not in your contacts. If you are expecting a call from a doctor, bank, or employer, you may want to turn off the filter temporarily or check your voicemail more often.
Understanding the privacy and security trade-offs
Blocking unknown callers improves your peace of mind and protects you from scams, but it also means missing legitimate calls. A recruiter calling about a job, a pharmacy confirming a prescription, or a delivery driver trying to find your address will all go to voicemail. You have to decide whether the quiet phone is worth the extra step of checking voicemail.
Third-party apps collect data about which numbers you call and which ones you block. Nomorobo and Whoscall use this data to improve their spam databases, but it also means your calling patterns are shared with a private company. If privacy is a concern, stick with your phone's built-in filter and your carrier's service, which keep your data within your phone company's systems.
Spam-blocking apps also require permission to access your contacts, call history, and sometimes your location. Review the app's privacy policy before installing it, and only grant the permissions it actually needs to function. An app that asks for access to your photos or location when it only needs to see your call history is a red flag.
What to do if blocking is not enough
If you receive dozens of spam calls per day even with all filters on, the problem may be that your number is on multiple spam lists. This often happens after a data breach, a public record search, or signing up for a service that sold your contact information.
Register your number with the National Do Not Call Registry at donotcall.gov. This is free and tells telemarketers they cannot call you. It does not stop scammers — they ignore the registry — but it reduces calls from legitimate companies.
If a specific company keeps calling, ask to be removed from their list. If they refuse or the calls continue, file a complaint with the FTC at reportfraud.ftc.gov. The FTC cannot stop individual callers, but it tracks patterns and can take action against companies that ignore do-not-call requests.
For scam calls specifically, do not engage with the caller. Answering or pressing a button confirms your number is active and may lead to more calls. Hang up and block the number. If the calls are threatening or harassing, contact your local police department and ask about filing a report.
Frequently Asked Questions
Will blocking unknown callers prevent my bank or doctor from reaching me?
Yes. Banks, doctors, and other businesses often call from numbers not in your contacts. If you have blocking on, these calls go to voicemail. Check your voicemail regularly, and if you are expecting an important call, turn off the unknown caller filter temporarily or add the number to your contacts beforehand.
Can I block calls from a specific area code?
Most phones do not have a built-in area code blocker, but some third-party apps like Nomorobo and RoboKiller let you block entire area codes or number patterns. This is useful if you know spam is coming from a particular region, but scammers often spoof local numbers, so it may not stop all calls.
What happens when I block someone — do they know?
When you block a number on your phone, the caller does not receive a notification that they are blocked. Their call fails silently on their end, and they may assume your phone is off or you did not answer. Blocked callers can still leave voicemail, though you will not be notified.
Is it safe to read a spam-blocking app?
Reputable apps like Nomorobo, RoboKiller, and Whoscall are safe, but review their privacy policies before installing. These apps need access to your call history and contacts to work, so make sure you trust the company. Avoid apps with poor reviews or those asking for unnecessary permissions like access to your photos or location.
Can I unblock a number if I change my mind?
Yes. On iPhone, go to Settings > Phone > Blocked Contacts and swipe left on the number to unblock it. On Android, open the Phone app, tap the three dots, go to Settings > Blocked numbers, and tap the X next to the number you want to unblock. You can block and unblock numbers as many times as you need.