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

Most phones let you block all calls from numbers not in your contacts, though the steps and what you see differ between iPhone and Android. On iPhone, you turn on "Silence Unknown Callers" in the Phone app settings — these calls still ring through to voicemail, but your phone stays silent and the call doesn't interrupt you. On Android, the process varies by manufacturer and carrier, but most phones have a "Block Unknown" or "Block Spam" toggle in the Phone or Messages app settings.

If you want to block specific unknown numbers instead of all of them, you can do that too — save the number to your contacts as "Spam" or "Do Not Answer," then use your phone's native blocking feature to block that contact. This is slower than a blanket block, but it gives you more control if you're expecting calls from numbers you don't recognize.

Carrier-level blocking (blocking through your phone company rather than your phone itself) is another option. Verizon, AT&T, T-Mobile, and most regional carriers offer spam-blocking services, some free and some paid. These work by filtering calls before they reach your phone, so you never see them at all — but they also mean you have no record of the call attempt, which matters if you're waiting for a callback from a doctor's office or government agency.

Key Takeaways

  • iPhone's "Silence Unknown Callers" sends unknown calls to voicemail without ringing your phone, and you can turn it on in Phone app settings under Calls.
  • Android phones have a "Block Unknown" or "Block Spam" setting in the Phone or Messages app, though the exact name and location depend on your phone's manufacturer.
  • To block a specific number, save it to your contacts with a label like "Spam," then use your phone's block feature to block that contact.
  • Your phone company (Verizon, AT&T, T-Mobile) offers spam-blocking services that filter calls before they reach you, though some charge a monthly fee.
  • Blocking at the carrier level means you have no record of the call attempt, so consider this if you're expecting calls from unfamiliar numbers.

How to block unknown numbers on iPhone

Open the Phone app and tap Settings (the gear icon at the bottom right). Scroll down and tap "Silence Unknown Callers." Toggle it on. From that point forward, any call from a number not in your contacts, recent calls, or Siri Suggestions will go straight to voicemail without ringing or showing on your screen.

This setting silences the call but doesn't delete it — you can still see it in your voicemail and call history if you look. If you want to block a specific number you've already received a call from, open the Phone app, find the number in your recent calls, swipe left on it, and tap "Block this Caller." That number will never ring through again, even if it's in your contacts.

How to block unknown numbers on Android

The exact steps depend on whether you have a Samsung, Google Pixel, OnePlus, or another brand, but the general path is the same. Open your Phone app (the one you use to make calls, not your contacts app). Look for a menu icon (three dots or lines) and tap Settings. Look for "Block numbers," "Spam protection," "Call screening," or "Block Unknown" — the name varies by phone.

On a Google Pixel, open the Phone app, tap the menu icon, go to Settings, then tap "Block numbers." You'll see an option to "Block unknown callers" — toggle it on. On a Samsung phone, open the Phone app, tap the menu icon, go to Settings, then tap "Reject calls," and look for an option to block unknown or private numbers. If you don't see these options in your Phone app, check your Messages app settings instead — some Android phones put spam blocking there.

If you want to block a specific number on Android, open the Phone app, find the number in your call history, press and hold it, and tap "Block number" or "Add to block list." The exact wording depends on your phone.

Blocking through your phone company instead of your phone

Verizon offers Call Filter (free version blocks spam calls; paid version adds more features). AT&T offers Call Protect (free version blocks known spam; paid version adds more). T-Mobile offers Scam Shield (free version blocks known scams; paid version adds more). These services filter calls at the carrier level, meaning spam and unknown calls are blocked before they reach your phone — you won't see them in your call history at all.

The trade-off is that you have no record of the call attempt. If you're waiting for a callback from a doctor, a government office, or a business you don't have in your contacts, carrier-level blocking might filter out the call you actually want. Check your carrier's website or call their customer service line to see what's available on your account and whether it's free or costs extra per month.

What happens when you block a number

When you block a specific number on your phone, that person can still call you — the call just won't ring through. It goes to voicemail (if you have voicemail set up), and they may or may not know they've been blocked depending on what message they hear. Some carriers play a message saying the number is not accepting calls; others just let it ring to voicemail like a normal missed call.

The blocked person can still text you, and the text will come through normally — blocking a number blocks calls, not messages. If you want to block texts too, you'll need to block the contact in your Messages app or use your phone's full contact-blocking feature, which blocks both calls and texts.

When blocking unknown numbers might cause problems

If you're waiting for a call from a doctor's office, a hospital, a government agency, or a business you've contacted, they may call from a number not in your contacts. Blocking all unknown callers means you'll miss these calls. Before you turn on "Silence Unknown Callers" or "Block Unknown," think about whether you're expecting any calls from numbers you don't recognize.

If you are expecting calls, you have a few options: turn off the blanket block temporarily, add the organization's main number to your contacts before they call, or use your carrier's blocking service instead (which lets you see a log of blocked calls). You can also ask the organization to call a specific number or to text you instead.

Third-party apps for blocking unknown numbers

Apps like RoboKiller, Nomorobo, and Whoscall offer additional spam-blocking features beyond what your phone or carrier provides. These apps use databases of known spam numbers and can block calls based on patterns (like calls from numbers that look spoofed). Some are free with limited features; others charge a monthly fee.

The downside is that third-party apps require permission to access your call history and contacts, and they add another layer of software to your phone. Your phone's built-in blocking and your carrier's blocking are usually enough for most people. Third-party apps are worth considering only if you're getting dozens of spam calls a day and the built-in options aren't keeping up.

Frequently Asked Questions

Will people know I blocked them?

Not necessarily. When you block a specific number, the call goes to voicemail, and the person may hear a message saying the number isn't accepting calls — or they may just hear a normal voicemail greeting. There's no notification that says "you've been blocked." If you use "Silence Unknown Callers" on iPhone, the person won't know anything happened; the call just goes to voicemail silently.

Can I unblock a number after I block it?

Yes. On iPhone, go to Phone Settings, scroll down to "Blocked Contacts," and swipe left on the number you want to unblock, then tap "Unblock." On Android, open your Phone app, go to Settings, find your blocked numbers list, and tap the number to unblock it. The exact steps vary by phone, but all phones let you unblock numbers.

What's the difference between blocking and silencing unknown callers?

Silencing (iPhone's "Silence Unknown Callers") sends unknown calls to voicemail without ringing your phone, but you can still see the call in your history. Blocking a specific number prevents that number from reaching you at all. Blocking all unknown numbers varies by phone — some phones silence them, others block them entirely.

Do I have to pay to block unknown numbers?

Your phone's built-in blocking feature is free. Your carrier's basic spam-blocking service is usually free (Verizon Call Filter free version, AT&T Call Protect free version, T-Mobile Scam Shield free version). Paid versions of these services and third-party apps cost money, but you don't need them to block unknown numbers.

If I block unknown numbers, will I miss important calls?

Possibly. Doctors, hospitals, government offices, and businesses often call from numbers not in your contacts. Before you turn on blanket blocking, think about whether you're expecting calls from unfamiliar numbers. If you are, ask the organization for their main number and add it to your contacts, or turn off blocking temporarily.