Anyone familiar with a 3Com NBX100 VOIP system?

[space-time]

I don't know about that system in particular, but I was able to unlock many Sunrocket VOIP boxes and then there are several free services where you can connect those boxes to test them, for example I use gizmo (aka sipphone) and make many free international calls this way. At some point I had 2 or 3 such boxes in my house when testing and I was making calls from one room to another just to test them (and tease the wife)

Good luck.