This might be interesting, about Nokia's ambivalence on VoIP
http://www.itworld.com/Net/3303/061129nokiavoip/
"On one hand Nokia is rolling out services that let phone users make free calls. Separately, however, it has been offering technology that can let operators decide to make the services low priority. "
and
"Last week, Nokia introduced Peer-to-peer Traffic Control, software that allows mobile operators to identify data traffic on their networks according to the type of service and then prioritize that traffic based on preferred services. That means operators can decide to make certain services, like VOIP, low priority so that if the network is full of traffic from more important services, the VOIP users won't get network access. "
I've read on other forums about people having trouble setting up the Nokia phone with their provider details. It seems that Nokia mainly envisaged wifi use in a corporate environment behind a company firewall, and aren't resolving NAT, ICE, STUN issues until sometime next year