Ex Altigen employee (albeit 6 years ago) here and have to say in comparison to the other software PBX's I have worked with it's a great product for both reliabilty, functionality and ease of use.
I don't think it's well suited to the UK market but in the US I think it's a great product.
I wouldn't want to compare it with other soft switches on here (just take my word for it it's the best
) but would like to make the comparison with the equipment I currently install: NEC/Zeacom.
The NEC is more reliable. It simply doesn't go wrong. All the clever stuff however is done using the Zeacom server. On a recent technical training course on the product I had to sit through half a days "features and benefits". All the other engineers were amazed at the products capabilities. For the record Zeacom does less than Altiserv did 6 years ago and does it less reliably. Zeacom's product is sold not only for NEC but also CISCO and AVAYA. The bottom line is that two things seperate these products. If an Altigen system crashes you're dead in the water. If a Zeacom system crashes (and it will) at least you still have dial tone.
If I was back in the states looking for a new phone system I would look no further than Altigen.