Can't dial any number

Hello.

I am newbie on Asterisk.
I added a Ericsson ipphone on Asterisk, but I can not dial any number.
I mean, I deal an internal ext. , the line opens and nothing more.
Incoming calls are OK.

Please, how can we solve this problem.
Thank you for your help.

to be able to call you must add your extension to the extensions.conf too. other then that i dont know.