Is there any way for me to register my friend with telephone numbers?

Lysn allows to send and receive a friend request through mobile address book.

Press Friend Tab - Settings button (on the upper right) - Register Friend.
If you press 'Allow friend request via contacts', then your friends who have your phone number can send a friend request to you.
If you put a check mark at 'An automatic friend requests to friends in your contact', then Lysn users in your address book will automatically receive friend requests from you.