How, using the Telegram API, send a message to a user by phone number?

Question

API

How can I send a message to a user on Telegram knowing only their phone number?

Answer 1

using the api bot - no way,
if you use the client api, then add yourself to your contact list, in response you will find out the user id. (stock up on sims for experiments, block at the slightest jamb, unblock only once, re-blocking is forever.

Answer 2

No way. Otherwise, spamming would be unavoidable.
The legal way is to write a bot or broadcast to a channel.