At least one other person has had this problem, but as far as I can see no solution was posted. So I will try again and ask for any ideas.
My P900 works fine, connects to Vodafone network and is able to send and receive SMS messages. However when I try to use it as a voice phone any number I dial recieves a number not known tone (series of regular beeps) and when I try to ring my phone I get a message saying that there is a fault and I should try again later. My SIM works fine in another telephone (not a P900) and other SIM's in my P900 give the same symptoms. It's as if the phone does not fully initiate itself into the network for some reason?
All other functions of the phone work fine.
Thanks in advance Seri.