Primary Account Identifier:
Unique Identity: Every single Telegram account is uniquely tied to one phone number. This number serves as your primary identifier on the platform. It's how Telegram distinguishes one user from another globally.
Non-Negotiable: You cannot create a Telegram account without a phone number. This is a fundamental requirement designed to combat spam and ensure a basic level of accountability.
2. Initial Registration and Verification:
Proof of Ownership: When you sign up, Telegram sends a verification code (via SMS, in-app message to another device, or to a Fragment +888 number) to the phone number you provide. Entering this code back into the app is the sole way to prove that you are the legitimate owner of that phone number.
Security Gate: This verification step acts as the initial security gate. Without access to the phone number to receive and enter the code, you cannot create or activate a Telegram account.
3. Login to New Devices (Session Authentication):
Core Authentication Factor: When you log into Telegram on a new device (e.g., a new phone, desktop client, or web version), your phone number is the first piece of information you provide.
Delivery of Authentication Code: Telegram then sends a new verification code. Crucially, the preferred method for sending this code is often to your active Telegram sessions on other devices (e.g., your primary phone where you're already logged in). This is a strong security measure, as it means an attacker would need access to your phone number and one of your existing logged-in Telegram devices. If no other active sessions exist, it falls back to SMS or voice call to the registered phone number.
Confirmation of Intent: By sending the code to your telegram number database number/existing session, Telegram confirms that the person attempting to log in on the new device is indeed you.
Second Factor: If you have 2FA enabled, your phone number acts as the first factor (receiving the initial login code), and your custom 2FA password acts as the second factor.
Protection Against SIM Swaps: This is where the phone number's role is critical but also where 2FA adds vital protection. Even if an attacker manages to perform a SIM swap (transferring your phone number to their SIM card) and can receive your SMS login code, they cannot log into your account without knowing your 2FA password. This password is never sent via SMS and is known only to you.