I've got a Trio 8800 with Visual+ (sw version 5.5.3.3517) registering to an Avaya phone system and to a Cisco VCS for video.
Video calls work fine. The unit can make telephone calls OUT fine. It can receive calls from outside and from internal analog/digital phones and Spectralink wireless phones fine. But if you call it from an IP-based internal phone it hangs up as soon as you hit answer.
Anyone experienced something similar?