g729 licenses not being used

I have all my phones, extensions and trunks set to use g729 1st then ulaw or alaw. For whatever reason it only seems to use g729 on about 20% of the calls. I have 8 licenses and only 5 users on a call at any given time.

This is an Asterisk 1.4.26 system running on centos 5.3 with a dual core and 2g of RAM.

No calls are being recorded.

What could be the problem??

can you do a CLI debug of a call setup so we can see what asterisk is doing with the SDP from the peer? Perhaps on 80% of the calls, the peer isn’t offering g729, so only ulaw matches.