First sort out the codec issue. It makes no sense to upgrade without knowing this will solve it, causing all kinds of new problems and then no way to go back.
You mention in post #1 it was working with a replacement german .31, however as I mentioned those german boxes do not have codec G729 on board. When you upgrade yours, you DO have G729 still on board. Seems that codecs are your problem.
By the way, I presume the audio was still absent?
I would like to have your box stop using G729, and when set to fixed network quality it should have. It's the middle of the three options.
What you need to do is check in the trace the sdp in the SIP Invite and 200OK messages. Does it mention pcmu/8000 or pcma/8000? Or something else?
Can you post the webgui page with the setting of the codec so I can have a look?
Next is, please check out the-construct.com. Later we could make a pseudo-image to set the order of codecs correct, and exclude G729.
By the way, maybe you can update your signature? So we may know your configuration?