You cannot block a call that shows no caller ID, but you can filter or silence it

When a call arrives with "No Caller ID" or "Unknown Number" on your screen, the caller has deliberately hidden their number — either through their phone settings or their service provider. Your phone's standard blocking tools cannot target something with no identifying information to block. Instead, you have three practical options: send unknown calls directly to voicemail, use your phone's built-in filtering system to silence them, or contact your service provider about network-level filtering.

The method that works best depends on whether you want to hear the voicemail message later, whether you're willing to miss legitimate calls from unknown numbers, and which type of phone you own.

Key Takeaways

  • Blocking requires a phone number or contact to target, so you cannot block "No Caller ID" itself — you can only filter or silence all unknown calls.
  • Your phone's native settings let you send unknown callers to voicemail on iPhone (Do Not Disturb, Silence Unknown Callers) and Android (Block Unknown).
  • Your service provider (Verizon, AT&T, T-Mobile, etc.) offers network-level filtering that stops many spoofed and hidden-number calls before they reach your phone.
  • If you need to receive calls from unknown numbers for work or medical reasons, filtering is riskier than using a separate voicemail greeting that discourages spam callers.

How to silence unknown calls on iPhone

iPhone has a feature called Silence Unknown Callers that sends any call from a number not in your contacts directly to voicemail. Open Settings, tap Phone, then toggle on Silence Unknown Callers. Calls from people you know will ring normally. Calls from numbers your phone cannot identify — including legitimate businesses, doctors' offices, and customer service lines — will go straight to voicemail without ringing.

This method works well if you rarely need to receive calls from unknown numbers. The downside is that you will miss calls from hospitals, schools, or services that call from main switchboard numbers not tied to a contact. Check your voicemail regularly, because legitimate callers will leave messages.

If you want more control, use Do Not Disturb instead. Open Settings, tap Focus, select Do Not Disturb, and toggle it on. Tap Allow Calls From and choose Contacts Only or Favorites. This silences unknown calls but still lets your phone ring for people you have saved. You can schedule Do Not Disturb to turn on automatically at night or during work hours.

How to filter unknown calls on Android

Android phones have a Block Unknown feature in the Phone app. Open the Phone app, tap the three-line menu (hamburger icon), go to Settings, then Call Screening or Spam Protection (the exact name varies by phone maker). Toggle on Block Unknown to send unidentified calls to voicemail.

Some Android phones also offer a Call Filter app made by your service provider. Open the Play Store, search for your carrier's name plus "Call Filter" (for example, "Verizon Call Filter"), and install it. These apps often let you choose whether to block, silence, or send unknown calls to voicemail, and they may catch more spoofed numbers than your phone's built-in filter.

Like the iPhone method, filtering unknown calls means you may miss legitimate calls from numbers not in your contacts. If you work in a field where unknown callers are common, this approach may not suit you.

Using your service provider's network filtering

Your carrier — Verizon, AT&T, T-Mobile, or another provider — can filter calls at the network level before they reach your phone. This stops many spoofed and hidden-number calls from getting through at all. Each carrier offers this service under a different name:

  • Verizon: Call Filter (free basic version, paid version with more features)
  • AT&T: Call Protect (free basic version, paid version available)
  • T-Mobile: Scam Shield (free for most customers)
  • Other carriers: Check your carrier's website for spam and scam protection options

To turn on your carrier's filter, log into your account on their website or call customer service. You can usually choose to block, silence, or send suspected spam calls to voicemail. Network-level filtering catches more hidden-number calls than your phone alone because it analyzes call patterns across millions of calls, not just your contacts.

The trade-off is that carrier filters sometimes block legitimate calls by mistake. If you are expecting calls from unknown numbers, ask your carrier whether you can whitelist specific numbers or turn filtering off temporarily.

Why callers hide their number and what that means

Legitimate callers — hospitals, government offices, and large businesses — sometimes show no caller ID because they call from main numbers that are not set up for caller ID, or because their phone system does not pass that information through. Scammers and spam callers hide their numbers deliberately to avoid being blocked or traced.

If you are expecting a call from a specific organization, call them back directly using a number from their official website or your records. Ask them to note your number so they can reach you, or ask for a direct line that will show up on your caller ID. This approach is safer than answering unknown calls and giving out information.

What to do if you answer a no caller ID call by accident

If you pick up and hear silence, a robotic voice, or someone asking for personal information, hang up when ready. Do not confirm your name, account number, or any other detail. Scammers use these confirmations to verify that your number is active and monitored, which leads to more calls.

Do not press any number to "remove yourself from the list" or "speak to a representative." Pressing a key tells the caller your number is real and monitored, and it often triggers more calls, not fewer. straightforward hang up and block the number if it shows up on your phone's call log.

If the call came from a number you can see, you can block it in your Phone app. Open the call log, find the number, and select Block or Report as Spam. This prevents that specific number from calling you again, though scammers often use different numbers each time.

When you should not filter unknown calls

If you are waiting for calls from hospitals, schools, job interviews, or services that use main switchboard numbers, filtering all unknown calls is risky. Instead, use a voicemail greeting that discourages spam callers without blocking legitimate ones. Record a message like: "Hi, you've reached [your name]. Please leave your name, organization, and reason for calling. I return calls from known contacts first." Spam callers often hang up rather than leave a message.

You can also ask the organization you are expecting a call from whether they have a direct line or a way to reach you that will show caller ID. Many hospitals and schools can call from a specific department number if you provide it.

Frequently Asked Questions

Can I block a specific person who is calling me with no caller ID?

No, because you cannot identify them to block them. If they call from the same number each time, that number will eventually show up in your call log and you can block it then. If they use different numbers or spoof their caller ID each time, your only option is to filter all unknown calls or let them go to voicemail.

Will blocking unknown calls stop my doctor's office from reaching me?

Possibly. Many medical offices call from main numbers that do not show caller ID. Before you turn on unknown call filtering, contact your doctor's office and ask what number they call from. If they cannot provide a direct line, ask them to note your number so they can reach you, or turn off filtering temporarily when you are expecting a call.

Does *67 hide my caller ID from the person I am calling?

Yes, dialing *67 before a number hides your caller ID on that single call. The recipient will see "No Caller ID" or "Unknown Number." Some businesses and government offices block calls made with *67, so the call may not go through.

Why do some legitimate businesses call with no caller ID?

Large organizations often have phone systems that route calls through main switchboards or automated systems that do not pass caller ID information to the recipient. Hospitals, government agencies, and utility companies frequently call this way. If you are unsure whether a call is legitimate, hang up and call the organization back using a number from their official website.

If I filter unknown calls, will I see them in my call log?

Yes. Filtered calls usually appear in your call log marked as blocked or silenced, depending on your phone's settings. You can review them later and unblock a number if you recognize it as legitimate. Some service provider filters also let you see which calls were blocked and why.