If trunk successfully configured but calls still failing then you need to confirm following parameters
1. Caller ID
Do gateway / provider impose any caller id format / pattern or require some fixed caller id, If so what is it ?
2. Dialing Prefix
Do you need to prefix outgoing calls with certain prefix ? And please also confirm if you have to dial 0, 00 Or 01, 011 ?
Do said gateway / provider require registration, If so what username and password combination you have to use ?