Your Phone Number Is as Important as Your Address
Your phone number is a direct line to you. Just as you would not hand your home address to someone you barely know, your phone number deserves careful handling. Once you have given a number out, you cannot take it back. If the other person takes a screenshot or pastes it into a group chat, it can spread all the way to people you have never met.
When a number gets around, you start seeing sales calls that slip past a nuisance call filter, and friend requests from strangers on social media. Read up on how personal information leaks out from a phone number, and then limit sharing to the people you can honestly say you trust.
Sharing with Friends Is Fine - But Set Yourself Some Rules
There is nothing wrong with giving your phone number to friends you trust. Keep the following rules in mind, though.
Tell Them Directly
Pass your number along in person or in a one-to-one message whenever you can. Posting it in a group chat or on a timeline spreads it to people you never meant to reach. Members you have never met end up with your number, and deleting the post does nothing about the people who have already read it or taken a screenshot.
Say "Please Do Not Pass This On"
When you share your number, add a line asking the person not to give it to anyone else. It sounds obvious, but if you never say it, people may assume that passing it along is fine.
Never Put It in a Social Media Profile
Do not write your phone number in your Instagram or X (formerly Twitter) profile. On a public account, even people who do not follow you can read your profile. On a private account, a follower can still copy the number down and carry it elsewhere. This is the most basic rule there is for protecting your phone number privacy.
Situations That Call for Extra Care
Someone You Met Online
Handing your phone number to someone you met in an online game or on social media is risky. You have no way of knowing whether they really are a friend your own age. Once they have your number, you may get relentless calls and messages, or find your personal information misused.
With online friends, the safe approach is to stay inside the messaging feature of the service where you met. If you really want to talk by voice, use something like a LINE voice call, which lets you speak without handing over your phone number at all. Our guide for first-time smartphone owners also covers how to deal with callers you do not know.
Prize Draws and Giveaways
Social media campaigns of the "follow and repost to win" variety sometimes ask for your phone number so they can contact the winners. Even when the message appears to come from an official account, think twice before sending your number by direct message. It may well be an impostor account.
Signing Up for Apps and Services
Apps often ask for a phone number when you register. If it is genuinely needed for SMS verification (identity confirmation), you have little choice, but when the field is optional you are safer leaving it blank. If you are registering a number for two-factor authentication, and the service also supports an authenticator app such as Google Authenticator, choosing the app is safer still.
Apps and services run by overseas operators are also covered by Japan's Act on the Protection of Personal Information, as long as they are offered to people in Japan. Article 171 of the Act states that it applies even where personal information about people in Japan is handled abroad, when that handling relates to supplying goods or services to people in Japan. In practice, though, there are situations that make the right hard to exercise: the enquiry desk may not operate in Japanese, or a deletion request may take a long time to answer. Check the terms of service and the privacy policy to see what your phone number will be used for before you sign up.
If Trouble Starts After You Have Shared Your Number
If someone you gave your number to starts calling relentlessly or harassing you, take these steps.
- Add that number to your call blocking list
- Save screenshots and your call history as evidence
- Talk to a parent or guardian
- Talk to a teacher or a school counsellor
- In serious cases, contact the police on #9110
You do not have to put up with it on the grounds that sharing your number was your own mistake. The person doing the harassing is the one in the wrong. Keeping evidence is what makes it possible to act later on.
What to Do When Your Number Has Already Spread
If a number you shared has travelled further than you intended and strangers start calling and messaging, work through the problem in stages.
- Start with call blocking: block calls from unfamiliar numbers one by one. Silence Unknown Callers on iPhone helps here. On Android, check whether your phone app or your telecoms provider offers something equivalent
- Work out where the leak came from: think back over who you gave the number to and reason out the route it travelled. If you posted it in a group chat, ask for that message to be deleted
- Review your social media settings: check whether people can find you by searching for your phone number, and turn that off
- Last resort - change the number: if blocking alone cannot keep up, changing the number itself is an option. The next section covers how to go about it
Changing Your Number as an Option
If the trouble simply will not go away, changing your phone number is a genuine option. The request goes through whoever holds your contract. How large the fee is, whether you can apply in a shop or online, and whether the switch takes effect the same day all vary by provider and by the terms of your contract, so check your provider's own guidance before you set anything in motion. Once the number changes, give the new one only to people you trust.
When you change numbers, remember to update the number registered with your bank accounts and with every service you use. Services where you have set up SMS verification are the critical ones: leave the old number in place and you may find yourself unable to log in. Drawing up a list before you make the change saves a lot of worry.
Treat LINE's Two Settings as Separate Things
There are two routes by which a phone number becomes a way in on LINE, and each is controlled by its own setting. Confuse the two and you may switch off one while believing you are covered.
- Auto-Add Friends: Settings, then Friends, then turn off "Auto-Add Friends" so you stop connecting automatically with the people saved in your phone's address book
- Allow others to add me: Settings, then Friends, then turn off "Allow others to add me" so that anyone who knows your number is far less likely to find you
Item names and where they sit can change between app versions, so if you cannot find one, search for it by name inside the settings screen. If you do want to connect on LINE with someone you gave your number to, adding them by hand with a QR code or a LINE ID is safer. Bear in mind, too, that these settings only change what happens inside LINE - they do not alter the fact that the other person knows your number.
In Summary
Giving your phone number to friends you trust is fine, but avoid publishing it in group chats or on social media. Do not share it with people you met online. When you do share it, ask the person not to pass it on. And if trouble starts, do not carry it alone - talk to an adult. Those are the basics of managing your number safely. It is worth reading through our detailed advice on managing phone number privacy as well.