The fastest way to block unknown calls depends on your phone type

Most phones let you block calls directly in the Phone app without downloading anything extra. On iPhone, open the Phone app, find a recent unknown call in your call history, tap the info icon next to it, and select "Block this Caller." On Android, open the Phone app, long-press the unknown number in your call log, and tap "Block number." Both methods stop that specific number from calling or texting you again.

If you want to block all unknown numbers at once rather than one at a time, your phone's built-in settings can do that too. iPhone users go to Settings > Phone > Silence Unknown Callers, which sends any call from a number not in your contacts straight to voicemail. Android users go to Settings > Call settings > Blocked numbers > Block unknown, which does the same thing. The trade-off is that legitimate callers you don't know — your doctor's office, a delivery driver, a callback from a job interview — will also go to voicemail.

Key Takeaways

  • Both iPhone and Android let you block individual numbers directly from the Phone app without installing anything.
  • You can block all unknown callers at once in your phone's settings, but this also blocks legitimate calls from numbers not in your contacts.
  • Third-party apps like Truecaller and RoboKiller add extra filtering but require permission to access your call history and contacts.
  • Carriers like Verizon, AT&T, and T-Mobile offer their own call-blocking tools, some free and some paid.
  • Do not call registries and blocking apps reduce spam but cannot stop all unwanted calls.

Using your carrier's built-in call blocking

Verizon offers Call Filter for free, which identifies spam and lets you block numbers. You can turn it on in the Verizon app or dial *72 to set up it. AT&T includes Call Protect free with most plans; turn it on in the AT&T mobile app. T-Mobile offers Scam Shield free, which blocks known spam numbers automatically. You can manage it in the T-Mobile app or by dialing #662#.

These carrier tools work at the network level, meaning they block calls before they reach your phone. That makes them faster than app-based blocking. However, the free versions have limits — they catch known spam numbers but miss new ones. If you want more aggressive filtering, each carrier also sells a paid version with extra features, though the free version handles most common spam.

Third-party apps for more aggressive filtering

Truecaller (free on iPhone and Android) identifies incoming callers and flags spam before your phone rings. It works by comparing incoming numbers against a database of known spam sources. RoboKiller (paid, around $4 per month) goes further — it answers spam calls with a bot that wastes the caller's time, which trains their system to stop calling you. Nomorobo (free on landlines, paid on mobile) blocks robocalls specifically.

These apps need permission to access your call history and contacts to work. Read what each app asks for before installing — some request more data than others. The trade-off is that third-party apps catch more spam than your phone's built-in tools, but they also require you to trust a company with your calling patterns. Test a free app first to see if it reduces your spam before paying for a premium version.

Registering with the National Do Not Call Registry

The National Do Not Call Registry is a free list maintained by the Federal Trade Commission. When you register your number, telemarketers are legally required to stop calling you within 31 days. You can register online at donotcall.gov or by calling 1-888-382-1222 from the phone you want to register.

The registry works for legitimate telemarketing calls but does not stop spam, scams, or robocalls from companies breaking the law. It also does not stop calls from charities, political organizations, or companies you have done business with recently. Registration lasts five years, then you can renew. Many people register and still get unwanted calls because the registry only covers legal telemarketers — illegal operations ignore it.

Why unknown calls keep coming and what actually stops them

Unknown calls come from a few sources: robocalls (automated systems calling thousands of numbers at once), spoofed numbers (callers hiding their real number behind a fake one), and legitimate businesses calling from numbers not in your contacts. Blocking and filtering reduce the volume, but they cannot stop all of them because new spam numbers appear constantly and spoofed numbers are hard to trace.

The most effective approach combines methods: use your phone's built-in "silence unknown callers" feature for peace of mind, register with the Do Not Call Registry to stop legal telemarketers, and add a third-party app if spam is still heavy. Do not answer calls from numbers you do not recognize — if it is important, they will leave a voicemail. Answering confirms your number is active and can increase spam.

Blocking calls on older phones and landlines

If you have a basic phone without a smartphone operating system, your carrier's call-blocking service is your main option. Call your carrier's customer service and ask them to enable call blocking on your account — most offer it free. Some older phones also have a built-in block list in the settings menu; check your phone's manual or call your carrier to learn how to use it.

For landlines, your phone company offers call blocking through your account. Verizon, AT&T, and other landline providers let you block numbers through their website or by calling customer service. You can also buy a standalone device like a CPF30 (Clarity) or ClearSounds CSC600 that plugs into your landline and blocks numbers automatically. These devices cost $30 to $60 and let you build a block list without relying on your carrier.

What to do if blocking is not enough

If you are getting dozens of calls per day even after blocking, your number may have been sold to multiple spam operations. Change your number through your carrier — most allow one free number change per year. When you change it, give the new number only to people you trust and avoid posting it online.

If the calls are threatening, harassing, or part of a scam targeting you specifically, report them to the Federal Trade Commission at reportfraud.ftc.gov. If they are extortion or threats, report them to local police. These reports help law enforcement track patterns and shut down operations, though they do not stop calls to your number when ready.

Frequently Asked Questions

Will blocking unknown callers stop me from getting important calls?

Yes, if you use "silence unknown callers" in your settings. Calls from numbers not in your contacts will go straight to voicemail, including callbacks from doctors, delivery services, and businesses. If you expect calls from people you do not know, use individual number blocking instead of blocking all unknowns.

Can I block calls from a specific area code?

Your phone's built-in tools cannot block by area code, but some third-party apps like Truecaller and RoboKiller let you block ranges of numbers. However, spammers often spoof local area codes to make calls look legitimate, so blocking an entire area code may not stop the spam you are trying to avoid.

Do I have to pay for call blocking?

No. Your phone's built-in blocking is free, your carrier's basic call-blocking service is free, and the Do Not Call Registry is free. Third-party apps like RoboKiller and some carrier premium tiers cost money, but they are optional — the free tools handle most spam.

What happens when I block a number — do they know I blocked them?

No. When you block a number, their call goes to voicemail or fails silently on their end. They do not get a notification that you blocked them. However, if they call repeatedly and get voicemail every time, they may figure it out.

Can I unblock a number after I block it?

Yes. On iPhone, go to Settings > Phone > Blocked Contacts and swipe left on the number to unblock it. On Android, go to Settings > Call settings > Blocked numbers, find the number, and tap the minus sign to unblock it. You can also unblock from your call history by tapping the info icon next to the number.