IPO 3.1 with a remote location with one IP 4610Sw phone. The phone has a display and buttons do work when pressed but no tone when speaker button is pushed or handset lifted. If you call the DID number corresponding to the extension it rings and connection is made but no audio. Ports opened on the routers are 49152 to 53246. Each router is on its own subnet. Any suggestions, the phone connects to the IPO fine.