I suspect by the poor quality of outbound sound on HSPA that it is either defaulting to ulaw (g711) or has the priority set as ulaw first.

I will try to do some more testing tomorrow to see what I can work out.

There is another issue with the VoIP system I noticed:
If you have more than SIP account registered and you select a name from the contact list it offers "phone" or "sip audio" numbers, but it does not tell you which sip account it is going to use.