Be sure to have H.263 support in H.320 standard. A common frustration to the caller is not knowing if the receiving station is busy or is not answering. It took us some time to realize that leaving a small self-viewing video window in a corner of the screen can impact receiving video performance due to the CPU being overwhelmed. A good example is the PC based VTEL system. The receiving window will look a lot better with higher frames per second when the self-viewing video window is closed.
Some system do fine with the self-viewing window on.
A PC-based system can be less expensive if you plan to add the video conference system to an existing computer with fast processing ability. Stand-alone equipment can operate for several years without requiring an upgrade, and ultimately may cause the fewest headaches. Intel Proshare 500 requires Netmeeting version 2.1 and is not compatible with the just released Netmeeting 3 on the same system.