I have discovered that my mobile phone N95 can be connected to my asterisk server and i followed a very good tutorial http://cook.dannemann.org.uk/howto/e61sip/ and all work.
but i have a problem when i try to call an extension from my mobile phone it’s impossible (i have an error message on my phone “adress busy” and it’s impossible to use the connection in this way.
i want to understand why it’s work in a way and not in the other
i want to know too if the problem is on the asterisk server or on the phone
thanks for your helpful help 
It is working fine here.
Working here, and in hotspots also, verify the status of the phone in the *CLI, and verify this:
Registration: Always On.
Also verify that you make an " Internet Call"