two simple checks just to start :

1) is the PC where the vt is installed connected to the IP phone's switch ? (it should)

2) Are the IP phones video enabled (flag in the device configuration page, you should see a little camera icon on the phone's display).

For debugging purposes you can double right click in an empty space on the vt window so opening the debug window. Check CDP Protocol, if the VT sends packets and if the phone anwers.

HTH

Alberto

if not