Why every app wants your phone number, and what it does with it

A dating app, a bank, a food ordering app and a loyalty card all asked for the same digits this year. They all had different reasons. But they weren't all telling the full truth.

Five things your number is used for

1. To prove you're a human Email addresses are cheap and limitless, phone numbers cost money, so they're a simple way to keep bots at bay.
2. To get back in Forgot your password? Sending you a text message is the fastest way for a service to get you back on board.
3. To log in Codes sent by text remain the most common form of second-factor authentication.
4. To find your friends Messaging and social apps will cross-reference the numbers in your address book with their own user bases.
5. To target ads The number can be matched to lists uploaded by advertisers, without needing to match up with your name.

The first three are normally explained in your account creation form. The last two are usually buried in the privacy policy.

When "for security" turned out to mean "for ads"

In 2022 the US Federal Trade Commission penalized Twitter $150 million.

Between 2014 and 2019, more than 140 million users submitted phone numbers and email addresses with the promise the information would safeguard their accounts. Twitter then used the same data to target advertising. And your phone number is the one thing you'll hardly ever change, which makes it particularly attractive.

Why a number is worth more than an email address

You can create a new email address in 60 seconds and even have a bunch of them. A phone number is not so easy. You use the same one for years, hand it out to your bank and the local pizza joint, and it gets connected to a human being. That makes it a great key for linking data that was independently acquired.

Numbers are "recycled", too. The carrier eventually will reassign the number to another customer. Reused numbers are so common that the US Federal Communications Commission runs a Reassigned Numbers Database for callers to check them, and nothing prevents those new owners from receiving your notifications.

A second number without a second phone

Giving out a separate number used to denote a second SIM, and arguably a second phone. Today the number can live in an app. It rings and takes texts as any number does, and you can turn it on and off without disconnecting your main number.

Typically, it's the price, and here is an easy way to get a free temp number. MoreMins has only one way to reach this, buy a US or UK virtual number, starting at $0.99 a month, and its buy one, get one code gives you a second UK or US number for a month for free. There is no charge for incoming calls and texts, and no one else can see them. It is not a free phone number, but it is close, and the minimal cost is what makes the number private.

One caveat. A temp phone number is for the long list of services that don't need to know who you are. Keep your bank and all your official contacts on your main number.

Three habits that cost nothing

• Check which apps can see your contacts and disable ones that have no business seeing them.
• If a service has an authenticator app and text messages, take the app. Your number won't matter so much.
• Chuck your number off a site when you stop using it, particularly before you give it up.

Questions about phone numbers and apps

Why do apps ask for my phone number?

To verify that you're a human being, to get you back into your account, to text you codes, to connect you with your contacts and, if they do, to target marketing to you.

Is it safe to give my phone number to an app?

For certain - if you need to identify yourself to a bank, for example. Otherwise a second number reduces spam and keeps your primary off marketing lists and data leaks.

Can I sign up without my real phone number?

Usually, yes. Most services will accept any number that can receive a text message or a phone call, so your secondary number in an app is fine. Your bank and other official services should remain on your real one.