I bought one of these a while ago to do training etc on and ran into a few problems but it was pretty good.
One particularly annoying stumbling block was I use SIP trunks and when a call got transferred to voicemail or to an auto attendant the call would go silent and drop.
There was an Early Adopter (7.1) update recently and now it all works! I've alo been playing with several other things that are not listed as features or even mentioned as supported but seem to be working.
So you have one box that does telephony (SIP, analogue or ISDN), firewalling, IPSEC and SSL VPNs (with accelerator) which comes with 4 analog extensions.
In New Zealand something like 80% or our companies have less than 20 people so these are ideal. Now that SIP things work they're even better!