Using NOKIAs VoIP Client since an E65 some years ago up to use this service in an N86 and now the N8 I observed this strange behaviour when setting up a new VoIP service:
Unfortunately the "Advanced VoIP Settings" for Symbian^3 seem to have a BUG compared with the earlier versions for earlier Symbian versions. I use an N86 and voip just works fine there - even over VPN tunneled to my home SIP and VPN server.
The bug is in the configuration of the SIP profiles / VoIP services.
On N86 you may first configure a SIP profile (incl. a single individual "default access point"), then switch to "Advanced VoIP Settings > create new service" and you will find there the newly created SIP account to activate as a "service".
Or you may do it the other way round: Go to "Advanced VoIP Settings > create new service" and configure there the basic data of your SIP profile (public user name and password). This creates a SIP Profile where you only need to configure either a "default destination" for access or a single individual "default access point".
Now, on N8 when I configure a SIP Profile first and then create the corresponding VoIP service I can do this - BUT TO THIS VOIP SERVICE I CANNOT LOGIN!
If creating the service the other way round > creating the VoIP Service and thus creating the corresponding SIP Profile in THIS SIP PROFILE NO INDIVIDUAL "DEFAULT ACCESS POINT" CAN BE CHOSEN - "INTERNET" IS PREDETERMINED AS "DEFAULT DESTINATION" AND CANNOT BE CHANGED (unless you configure also VPN - in this case you can also choose "intranet" instead of "internet").
The possibility to configure an individual "default access point" in a SIP Profile is in certain circumstances important when using VPN!