This is pretty much a standard video conference client. Most products from other companies will work with this. For Windows and Linux computers you should also be able to use ekiga as an open source software client (you will need speakers, webcam and microphone to make this work).
If you have never used video conferencing before, then you will probably have a bit of a learning curve with the firewall settings and communication setup. I would suggest to either buy a kit that comes with installation and training, or first try some internal video conferencing using ekiga (this will further your understanding of call setup).
We have video conferencing equipment from Polycom, and we have done many calls to clients who use all sorts of kit, possibly including Tandberg. In most cases you won't even know. We only use VC over IP connections, i.e. no telephone lines, but both is possible (if you have enough trunk line capacity).