Unwanted calls are often harmless but some are after your credit card information, IDs or passwords. All are a distraction and a waste of your time.

Robocallers have gotten more devious by masking their calls with phone numbers that use the first three or first six digits of your phone number.

But the scams are old. They pretend to be major banks, big tech companies, or government organizations like the IRS.

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Whatever the scam, here are several ways to stop unwanted calls on your smartphone – and one way to stop them cold.

Manually: if you don’t get a lot of unwanted calls, you can block calls one at a time. On the iPhone you do this by selecting “Phone” then tapping the information icon (the encircled lowercase “i”), and selecting “Block this Caller.” On Android, it’s similar, you tap on the caller’s name, then long-press the number and tap “Block/report spam” (note that this procedure can vary slightly from device to device on Android).

Blocking calls manually, however, is usually futile because scammers and spammers are constantly changing their numbers, usually on a daily basis.

Use an app: there are lots of apps that take on telemarketers and suspicious calls, some are better at blocking calls before they get through than others. AT&T and Verizon, as with other carriers, offer apps that let you block calls by identifying likely fraudsters. To identify a suspicious call, numbers are run against a massive list of robocallers that is updated daily.

For instance, the basic setup of the Verizon Caller Name ID app ($2.99 per month per line) is like any call blocker app on the iPhone. After installing the app, under the iPhone’s Settings you tap on “Phone,” then “Call Blocking & Identification,” then toggle on the Verizon “Caller Name ID” app.

If you want to take this a step further, the Verizon app will also try to block suspicious calls and send them to voicemail. This requires going into the Verizon app and tapping “Block” then “Spam filter on” then setting a risk level.

For Android devices, you open the Verizon Caller Name ID app, tap “Block management,” tap “Spam filter”, then toggle the feature on and select the risk level.

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AT&T has its Mobile Security & Call Protect Plus ($3.99 per month) service that has Automatic Fraud Blocking, which can detect and allow you to block incoming suspicious calls.

Samsung offers a “Smart Call” feature on its phones that can tell you if the call is suspicious and allows you to block the call. Go to “Caller ID and spam protection” in Call Settings, then turn on “Caller ID and spam protection.” Note that is not made available by all carriers.

And Google offers caller ID & spam protection for Android. With this, you can stop spam calls from ringing on your phone. "You won't get missed call or voicemail notifications, but you'll still see filtered calls in your call history and be able to check any voicemail you receive," according to Google.

There are third-party apps that you can try for free such as Nomorobo and RoboKiller. After the trial period, both ask for a small monthly fee, which typically starts at $0.99 or $1.99 per month. There’s also an app called Hiya that is free.

The best advice is to try these services and see which one works for you.

Kill all suspicious calls: the most effective method is to limit calls to your contact list. On the iPhone, this will stop all unwanted calls from ringing on your phone. The only calls that get through are people on your contact list. Other legitimate calls typically go to voicemail.

On the iPhone, you go to Settings, then tap on “Do Not Disturb” then select “Allow Calls From” then “All Contacts.” This is deadly effective and may be a good option for people hounded by spam calls. For Android, you can do this with apps such as Calls Blacklist.