Our Netvanta 7060 and Adtran IP712 phones have been having this problem over the last few weeks. Outside callers call our internal phone numbers/extensions and normally when they hear the voicemail prompts to leave a message, silence is encountered or only a click or two. The user leaves a voicemail anyway, which does record and show up in both the phone's voicemail inbox and the email feature, but the audio is completely missing. The length of the message is still correct (x number of seconds long), but it's just blank with no sound at all.
This happens seemingly randomly.
The only thing I can think of is we had a brown out about a month ago and our TotalAccess 908e that our phone company uses froze up on us and had to be rebooted. We also asked the phone company to replace that TA908e, but that did not solve this problem.
In addition, the autoattendants no longer play/trigger at all, but that is a separate post...
In addition, we also just replaced our entire Netvanta 7060 with a replacement unit (swapped over the CF flash cards and imported the config file) and it's doing the exact same thing.
The issue is likely related because AA and VM use the protocols and portions of the system to work. Please see you other post for some additional troubleshooting steps I provided there.