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 ?
Which codecs they support ?
And there are few things which you have to check from gateway side
i). IP Authentication
Confirm server IP is authorized to make calls, and is associated with right account
ii). Call Routing
Confirm if your local prefixes allowed and there are proper route for them