The latest beta versions of Telegram for iOS and Android allows you to sign in to your account with email, Apple ID, or Google. This is reported by the Telegram channel Beta Info.
At the same time, registration will still be available only by phone number, but for re-entry, you can link your Apple or Google account — or receive a code by email.
This authorization method will be useful to log in to your accounts in different places where you don't have access to your phone number. You can choose a new authorization method in the privacy settings of the messenger. As for now, this feature is only available in test servers.