[Linphone-users] Account with only numbers in username: is it possible ?

[gegetel]

Hello,

I am trying to create a free sip account on linphone.org for using this 
account with an user-agent (speedtouch modem) that can only dial numbers.
In the Username field I enter 77335500, a good password in Password fields 
and my true e-mail in the E-mail field, then clic on Create button.

But I only get this error message in red letters:

"Username is incorrect (should contain lowercase alpha, numbers, and . _ - 
only)."

What is my error ?