We just installed our Lab environment an everything appears to be up and running we have 6 phones hooked up to it, an IP 655, 2-IP 485’s 2 480’s and a 420. When we call from extension to extension the phone will ring but as soon as you answer it disconnects and goes back to dial tone. We also made an AA to try and test call, from the 655 the call completes to the AA from any other IP 485, 480 and 420 they do not complete same thing happen as extension to extension.
I would suspect a routing issue – calls set up (ring) but when connected – the phone audio is not routing correctly phone to phone (and they need to route voice packets directly phone to phone). I would check to make sure you don’t have more than one Gateway IP in the routing path.