I got the same problem too!! Can hear the phone ringing, Then NO AUDIO.
I'm using a UK SIP provider and have been for years.
How to solve this PLEASE HELP me.
Thanks Robert
UPDATE :
After years of no issues... following the RECENT Google voice updates etc (i don't / can't use Google Voice anyway) I set the DMZ option in my router pointing at the STATIC IP Address of the Obi 200.
ISSUE SOLVED!
It can also be solved by forwarding the UDP ports used in the RTP Profile (LocalPort Min - LocalPort Max RANGE) in your router. My sister has also the same problem - different models of TPLINK ROUTERS
It would have been helpful if Polycom would have offered some guidance to their users....
It's not all about Google Voice, some of us use other VOIP services.
I had spent DAYS on this! - was about to put the lot in the bin!
Hope this will help some other poor souls with similar issues.