Moving ATA configuration to a trunk

I have setup my Linksys ATA to use the long distance VoIP provider. Everythign works just find. I setup the proxy, username, password, codec, …

Now, I want to move this to FreePBX and be able to use that provider for any long distance call made from any extension. I tried to move this setup to a trunk, as a peer only, but it does not work!

How can I use the ATA setup which is working from an ATA, to FreePBX to be able to use many extension?

Asterisk must be at least as capable as an ATA box!