Using a combination of posts from different forums, I've finally got SIP working on my
N95 8GB via VoipStunt! Thanks mthompson for the final piece of the jigsaw.
For the sake of others searching after me, it started with "unable to connect to connection server" error.
Here are the settings, including mthompson's advice about UDP/TCP, that got me up and running. For the record, I'm on the 3 network.
Service Profile: IETF
Default access point: Your preferred wireless network
Public username: sip:[username]@voipstunt.com
Use compression: No
Registration: When needed (use always on if you want it to stay connected all the time)
Use security: No
>Proxy server
>>Proxy server address: sip.voipstunt.com
>>Realm: voipstunt.com
>>Username: voipstunt username
>>Password: voipstunt password
>>Allow loose routing: Yes
>>Transport type: UDP
>>Port: 5060
>Registrar server
>>Registrar server address: sip.voipstunt.com
>>Realm: voipstunt.com
>>Username: voipstunt username
>>Password: voipstunt password
>>Allow loose routing: Yes
>>Transport type: TCP
>>Port: 5060