I'm having a strange problem with my new Nokia N73.

A lot of the time when someone tries to ring me they just get a message
saying "Sorry, we cannot connect your call, please try again later". I look
at my phone and it has a full signal.

From what I can assertain it seems that if I leave my phone in my house for
any period of time it stops accepting calls and texts even though there is a
full signal. However if I then make an outgoing call using the phone, then
incoming calls and texts start working[1], for a period of time, and then
stop again.

[1]I often end up getting text messages in the middle of calls because of
this.

I figure I'm going to need to call O2 about this, but I'm not exactly sure
what to tell them!