You can move your account to a new number and keep everything: contacts, messages, media in the cloud, and even your Secret Chats on every device. Nothing is lost and nobody has to re-add you.
How to do it
- Open Settings.
- Tap your phone number, shown just above your username.
- Choose Change Number.
- Enter the new number and confirm it with the code sent to it.
What happens to your chats
The account itself moves, so every conversation continues where it was. People who have your new number saved will see you under it automatically. People who only have the old one keep the existing chat, since the conversation belongs to the account rather than to the number.
The one blocker
If a different Telegram account already exists on the number you are moving to, the change will not complete. You have to delete that other account first, which removes its messages permanently. Check what is on the target number before you start, not after.
Do this before you lose access to the old number
Changing the number requires confirming the new one, so a SIM you no longer control is not itself a problem. What does cause trouble is losing access to the account entirely first. If you are switching carriers or countries, change the number while both are still reachable.
Updated