The ability to manage your trunks from the perspective of load balancing, and cost balancing, is largely absent from FreePBX and Asterisk.
I am pleased to announce the availability of the second alpha version of the trunk cost balancing module for FreePBX. http://projects.colsolgrp.net/projects/show/trunkbalance
The primary discussion thread for the module is here: http://pbxinaflash.com/forum/showthread.php?t=6146
Trunk balancing is a program designed to manage the availability of outbound trunks based on number of minutes used, and number of minutes available. This module is used primarily to help users create a "least-expense" route environment. It can also balance the load on multiple outbound trunks by applying a ratio factor.
If your outbound trunks include a certain number of outbound minutes, and then charge by the minute -- or if you simply want to control the load on your trunks via a ratio setting, this module may have just what you've been looking for.
Remember -- Alpha revision software should not be applied to production, or mission-critical PBXs.
Why not drop by, and kick the tires on this new exciting module for FreePBX.