No. What is the outbound proxy for the ISDN trunk? It should be something like 127.0.0.1:5062 if the gateway listens on port 5062.
The outbound proxy: 127.0.0.1:5062, that's correct.
Also what is the user dialling? Something like 06912345 to get a number in Frankfurt?
the user is dialing a 06 number in the netherlands