How to Prevent Spam Callers From Leaving Voicemail

Blocking of spam callers has gotten better, with many carriers implementing STIR/SHAKEN (more on that below) and other carrier-based methods of preventing spam callers before they ever ring on your phone. But even with the newest technologies, it's clear from comments from our readers and our own experience that plenty of spam callers are still getting through. And if you don't answer those calls, they'll fill up your mailbox with sketchy messages about your car warranty or vacation club offers.

Unfortunately, preventing spam callers from leaving a voicemail on your cell phone can be tricky. We've researched the options from each carrier and tested a number of call blocking apps to see what really works. Here are the solutions we've found for blocking spam calls and voicemails directly through your phone, via your carrier or a third-party app, and the features and limitations of each method.

Blocking Calls on iPhones (but not voicemail)

On iPhones running iOS 8 or higher, go the Recent Calls tab in the Phone app, tap the “i” icon at the right of the number that you want to block. If the number is in your Contacts list, open that contact’s page in the Contacts app. From the contact page for the caller or contact, scroll to the bottom of the page and tap Block This Caller.

But this method has two drawbacks. First, someone has to call you in order to block the number. And since spammers rarely use the same number, or use the “neighborhood spoofing” technique (where they use your area code and three number prefix), this won’t block the majority of spam calls we get. Second, those blocked calls still go to voicemail, though theses voicemails show up in a "Blocked Messages" folder at the bottom of your list of voicemails and you won't get a notification.

You can also choose to silence unknown callers – anyone who is not listed in your iPhone's Contacts. Your iPhone won't ring, but the calls will show up in recent calls and you'll see voicemail in your regular voicemail inbox.

Blocking Calls on Android Phones (and voicemail on Pixel)

Android has built-in call blocking, similar to iOS. Just tap a number in your call log and hit Block/report spam. And like Apple, this method has the two same drawbacks – the spammer has to call your first and blocked callers still go to voicemail.

Android also has the option in the Phone app settings to automatically identify and block suspected spam calls so they don’t ring your device. It should be on by default, but you can check by going to "Settings" in your Phone app, then "Spam and Call Screen," and make sure the " See caller & spam ID" is toggled on. This feature still sends those calls to voicemail, however.

If you have a Google Pixel phone, you can choose to have Google Assistant answer a suspected spam call and transcribe the conversation in real time, so you can decide if you want to answer the call or hang up. And since Google Assistant already picked up the call, hanging up won’t send it to voicemail. To turn it on, go to "Settings" in your Phone app, then "Spam and Call Screen," and make sure the " See caller & spam ID" is toggled on. Tap "Call Screen." Under “Unknown call settings,” tap the types of callers you’d like to screen "Spam," "Possibly faked numbers," "First-time callers," and "Private or hidden."

Spam Blocking Apps for Android & iOS

There are dozens of apps in the Apple App Store and Google Play that are labeled as call blockers. But you have to be very careful about which you install – you’re giving them full access to your phone, texts, contacts and more, meaning there’s a lot of potential for misuse. And each of those apps will only perform as well as the technology (and the blacklist) running it. Also, while these apps will block calls, because of restrictions placed on apps by the Android and iOS operating systems, most won't stop those calls from going to voicemail.

However, the Call Control app for Android will actually block robocalls from leaving voicemail. Calls on your blocklist, neighborhood spoofing calls and calls identified by Call Control's community blocking are simply dropped – no ring, no mailbox filling up with crap you have to delete. At $29.99 per year, it's not cheap, but that's in line with other major call blockers, such as Hiya or Truecaller, that don't offer the voicemail blocking capabilities. Call Control does have a free offering, which blocks neighborhood spoofing numbers but not numbers on the community blocklist; if most of the calls you receive are of that variety, you can get away with this option.

Unfortunately, Call Control for iOS doesn't offer the voicemail blocking because of limitations Apple puts on iOS device access, so you're probably better off with Hiya& or Truecaller, who have larger community blocking lists. Personally, I prefer Hiya which white-labels its technology to Samsung, AT&T and others, has an extensive community-driven blacklist, allows you to block neighborhood spoofing calls, and even provides caller ID features that you would usually have to pay for with your carrier. Hiya is $2.99 per month or $14.99 per year.

Blocking via Google Voice

Google Voice provides another way to block pesky spam calls and prevent them from going to voicemail. The trick is you need to switch to Google Voice as your main number and stop giving out your old carrier number. With Voice, you can block known spam calls in three ways: by sending calls to voicemail, by treating the call as spam (letting the caller leave voicemail but tagged as spam) or by call blocking (in which case the caller will hear a “Number not in service” message and will not be able to leave voice mail).

The big drawback here is that your Google Voice number now becomes your main number, which you forward to the number from your carrier, and you need to use the Google Voice app as your main calling app on your phone. And there’s still no guarantee that spam callers won’t call your carrier number directly, either because it’s already out there (learn how telemarketers get your number) or simply because the robodialers are going through every number combination.

Carrier-level blocking

Truly effective call blocking and voicemail prevention needs to be at the carrier level – it’s the carriers who have the technical capability to identify call origination sources and create services that prevent spam and blocked calls from going to voicemail (since they’re the ones that control the voicemail service). Under the TRACED Act that took effect last year, carriers can now finally block suspected spam calls before they reach your device.

The FCC has also been working with carriers for years to deploy a technology called STIR/SHAKEN, which authenticates calls. When a call originates, the caller ID is "signed" as legitimate and is validated each step of the way, as it moves from network to network, before reaching you. The major carriers have implemented STIR/SHAKEN and are starting to show when a number has been verified. This can show up as a "verified number," "caller verified," or "valid number." On iPhones running iOS 13 or higher, you'll see a check mark under calls in your Recent Calls list that have been verified. Right now, the lack of these verification labels doesn't mean that the number is spoofed. It just means that numbers with the tag have successfully validated all the way through the call routing and you can know the number isn't spoofed.

Soon your carrier may start blocking calls that haven't been validated. According to a recent FCC statement (PDF document), "Beginning on September 28, 2021, if a voice service provider’s certification does not appear in the database, intermediate and voice service providers will be prohibited from directly accepting the provider’s traffic." This could be a big advancement, since nearly 95 percent of all robocalls originate on small networks, according to a recent study by Transaction Network Services, an anti-robocalling technology company. We will have to see how the robocallers adapt.

In the meantime, all the major carriers offer various flavors of spam blocking services, some free and some which you have the privilege of paying extra for.

Call blocking on AT&T

At a basic level, AT&T postpaid customers can activate AT&T’s free Call Protect service on their accounts with the Call Protect app. Call Protect will block known spam calls entirely, preventing them from leaving a voicemail, and let you block specific numbers. You'll also see "Valid Number" if the call has been verified.

If you want more features, you can upgrade to Call Protect Plus for a pricey $3.99 a month. Call Protect Plus users can block categories of calls, including: private callers, political calls, telemarketers, account services, and general spam. You can choose to have these calls go to voicemail or be blocked entirely. And, you can do reverser number lookup, to see who's calling

Call blocking on T-Mobile (and Sprint)

Even though T-Mobile and Sprint have merged, call blocking is still handled separately.

T-Mobile customers can download and use the free Scam Shield app to be notified when scam calls come in or block spam calls and prevent the caller from leaving a voicemail. You can also turn on T-Mobile's scam blocking by dialing #662# and pressing the call button. You'll also see "Caller Verified," if the call has been verified.

For $4 a month, Scam Shield Premium lets you send categories of calls, like telemarketing calls, survey calls, political calls, and charity calls, straight to voicemail. And, you can do reverse number lookup, to see who's calling.

Former Sprint customers can use the free Sprint Call Screener app, which comes preloaded on most Android phones and can be downloaded for iPhones. The app automatically identifies callers and will show verified calls as "Verified Number." You can also set up a personalized call blocking list.

Call blocking on Verizon

Verizon's Call Filter service offers spam blocking for free. You'll get a warning of incoming likely spam and can send those calls to voicemail. With the app, you can block spam calls by risk level (either send to voicemail or hang up), report calls to improve Verizon's community blocking list, and add neighborhood spoofing protection. For $2.99, you can get Call Filter Plus, which offers more advanced caller ID, including viewing incoming-call risk level, and reverse number lookup features.

While all of the options above will help you block calls and, in some cases, stop spammers from leaving a voicemail, the best way to prevent these calls in the first place is to learn how telemarketers get your cell phone number – and then don’t let them have it.

[Image credit: scam call via Shutterstock]

Updated on 7/15/2021 with new recommendations

Josh Kirschner is the co-founder of Techlicious and has been covering consumer tech for more than a decade. He covers privacy and consumer protection issues, as well as anything that ties into his passion for food and cycling.