"Sync Contacts" (Under Data Settings or Contacts):
ON/OFF Toggle: You control whether Telegram accesses your device's address book to upload phone numbers and names to its servers. If enabled, Telegram uses this data to identify which of your existing contacts are also on Telegram, making it easier to find and message them.
Privacy Note: Telegram explicitly states it only stores the phone numbers and first/last names for this purpose, not other contact details.
"Delete Synced Contacts" (Under Data Settings or Contacts):
If you've previously synced contacts and wish to remove them from Telegram's servers, you can use this option. Even if you disable "Sync Contacts," previously synced contacts remain until you explicitly delete them.
III. Discoverability via Usernames
Username Creation: You control whether you set a @username for your Telegram account.
Anonymity: If you create a username, people can find and contact you using that username without ever needing or seeing your phone number. This is a powerful privacy tool, especially if your phone telegram number database number visibility is set to "Nobody."
IV. Interaction Controls (Who can reach you)
These settings determine how other Telegram users can initiate contact with you.
"Groups & Channels":
"Who can add me to group chats?" You can choose:
Everybody: Anyone on Telegram can add you to a group.
My Contacts: Only people in your Telegram contacts can add you.
Exceptions: You can specify "Always Allow" or "Never Allow" for particular users, overriding the general setting.