Hi.
I'm not sure how easy it would be to run an instance of asterisk inside the N9 but if that is the case I would open an GPRS/UMTS ip connection and use it as the outgoing trunk. You would need a voip account to connect to, but configuration should certainly be easier.
I'm supposing that you would use the phone's Wifi as a hotspot for the VOIP clients, right?
Regards.