Privacy concerns, if you're important enough.
Serj.Just a small warning:
If you are important enough that someone is willing to find your phone number, you should know that there are people slowly "bruteforcing" their way in telegram.
How it is possible, theory first:
1. Telegram (and other messengers that use phone number and have public groups) can show you, if people in your contacts are using telegram so that you can write them.
1a. If you check your contact profile, you can see their number, since you have it.
2. Users in telegram have a unique number so that personal messages can work etc even if you change your name and username (e.g. my id is 361565, and every my message is signed "written by 361565", and if I send someone a pm, it is a pm from 361565.
2a. If you delete your account and create it again (👀 kamran), you will have a new id. Old messages in groups and pm are still signed by old id (without user) so they will have "Deleted Account". New user have a new id, so if they pm you, it is going be a new chat from a new id (you won't see old messages there, and they don't have messages either - old messages were written by "another user" (=old id, that is now Deleted Account)
How-to:
3. A person buys (a shitton of) simcard. Adds 200-5000 contacts from +0...00000 to +00...05000. Logins to telegram.
Telegram checks (as it is supposed to) if your contacts are using telegram, and if they do - sends you their ID (with some other things), so you would know when they pm you, for example.
Of course there are limits, speed limits, bans etc, but eventually you will have a list of ids and telephone numbers of those ids. You put them into a database, probably delete and re-create your telegram account with another 5000 contacts, and there are also speed limits (~1 change per week? No more than 5 times? Something like that).
The speed is not great and you really need A LOT OF sim cards, but it's doable.
So at the end if you want to know a telephone number of a user you see somewhere (in a group, channel, or if you have a message forwarded from that user - it is signed by their id), you can check their id in your database and there is a chance it will be there with a telephone number.
There are bots that try to lure people into sending them their contacts (just like truecaller shit) to gain some points you can spend to see someone's phone number, and those bots are banned by telegram on sight.
But nothing stops bad guys from creating websites for the same purpose. (And getting contacts helps them to get more popular numbers first, because starting from +00...000 is pointless)