asterisk users - Jun 2013 - Implementing G729 Passthrough - VM recordings, maybe even a2billing

We would like implement G729 passthrough for our calls and get rid of
the encoding overhead, and a little confused as to how to do this, and
some unanswered questions. Do we need the open source G729? If so, do
we still need the patent license. Not so much of an issue, just
checking. Finally, a recent howto of how to enforce pci passthrough
and disable encoding would be greatly appreciated.

Oh, and there is also the issue with VM recordings, message etc.. On a
slightly unrelated, we are using a2billing on some of our machines,
and I think that we would have to convert that media from slink to
G729 if not done so already...

Thanks in Advance,

Nick.