Unique and Immutable: Every Telegram account (and every chat, group, or channel) is assigned a unique, numeric User ID by Telegram's servers at the time of creation. This ID is an internal identifier and generally remains constant for the lifetime of the account.
Decoupled from Phone Number Changes: A crucial aspect of the User ID is that it does not change if you change your phone number associated with your Telegram account (using the in-app "Change Number" feature). Your existing account and all its data simply migrate to the new phone number, but the underlying User ID stays the same.
Backend Operations: Telegram's servers primarily use User IDs to route messages, manage chat histories, and identify users in its internal systems.
Bot Interactions: Telegram Bots heavily rely on User IDs (and Chat IDs for groups/channels) to send messages to specific users or chats. When you interact with a bot, it receives your User ID.
API Calls: Developers interacting with Telegram's API use User IDs to programmatically manage users, send messages, and perform other actions.
Deep Links: Some Telegram deep links (e.g., tg://user?id=123456789) can directly link to a user's profile using their User ID.
Not Directly Visible to Users (Typically): Unlike usernames, the User ID is not prominently displayed in the Telegram app interface for regular users. You usually need to use a specific bot (like @userinfobot or @RawDataBot) to find your own User ID or the User ID of others (if you have their username).
The Interplay:
Creation: A phone number is used to create a telegram number database new account, and in that process, Telegram assigns a unique User ID to this newly created account.
Authentication vs. Routing:
Phone numbers are for authentication and identity verification at the point of login or recovery. They establish who you are.
User IDs are for internal routing and identification after you are authenticated. They tell Telegram's system where to send messages and who corresponds to which data.
Privacy Layering.