How to know the client’s number in Telegram and Facebook* Messenger?

How to figure out client's number on Telegram or Facebook* Messenger?

You can request the phone number of a Telegram and Facebook* Messenger client. To do this, click the button next to their ID in the chat header.

The client will receive a standard request for the number sharing. 
 

His phone number will appear as a button. If the client clicks it, the phone number will be displayed in the "header" instead of the ID, and the operator will receive a service notification.