Looking at http://dl.fedoraproject.org/pub/epel/6/x86_64/ I see that we have asterisk 1.8 packages.
I took the src.rpm from http://dl.fedoraproject.org/pub/epel/6/SRPMS/ and see that:
[mihamina centos6-01 SPECS]$ grep -n g729 asterisk.spec
2969:- g729 licenses from being freed up.
A long time ago I had to manually import the g729 binary from http://asterisk.hosting.lv/:
Is the codec bundled in EPEL asterisk way different from the prebuilt with IPP?