I configured my Nokia E71 phone to use my SIP account with budgetphone.nl, a local VoIP provider. I used the following settings:

Settings -> Connection -> SIP settings

Profile name: Budgetphone
Service profile: IETF
Default access point: KPN UMTS
Public user name: sip:31107142219@budgetphone.nl
Use compression: Yes
Registration: Always on
Use security: No
Proxy server: <not configured>
Registrar server:
Registrar server address: sip:sip.budgetphone.nl
Realm: budgetphone.nl
User name: 31107142219
Password: <my password>
Transport type: Auto
Port: 5060

Settings -> Connection -> Internet telephone

Profile name: default
SIP profiles: Budgetphone

The account registers succesfully, and I can receive calls on my VoIP account. However, whenever I try to make an outgoing call to a phone number through VoIP (Options -> Call -> Internet call), it tries to call to <phonenumber>@sip.budgetphone.nl and returns the message:

internet telephone service not available

This makes sense to me, as the number I try to call does not exist at sip.budgetphone.nl. When I try to call a number that DOES exist at budgetphone.nl, it indeed works. However, it is unclear to me how I should call a phone number through SIP.

Some additional information:
- It does work for me when I use a software SIP application on my computer
- It is no restriction with my UMTS provider; I tried it both with wireless and UMTS

I'd really like to get this to work, as I bought my phone without a plan.