We have setup the IP phone proxy on our ASA-5520, we had a couple of issues with the initial setup, but nothing major. It has been up and running for a few weeks and basically everything works perfectly just like we designed it except for 1 strange audio issue on outbound calls. We can make a call to anywhere, no problem, if the call is answered, no problem, perfect call setup and good quality 2 way audio. But if the person we called doesn't answer the call and that call goes to their voicemail we loose all audio from that point forward, we do not hear their outgoing message or get any prompts just dead air. The same situation appears to be true for any "recorded" service on the other end of the call.
If anyone has heard of this issue or can offer some troubleshooting guidance, it would be greatly appreciated.