I agree with the bulk of the comments posted here about so-called "pure IP" solutions. My experience has been that they're either too complicated as server-based systems (and I come from the IT side) or/and offer no overriding savings. Just recently I had to pull out an Asterisk installation and retrofit the customer's otherwise perfectly working Nortel TDM system (for which the Asterisk was running as a SIP gateway).
The problem was SIP bugs, compounded by not exactly reliable service from the SIP provider. The customer had insisted on Asterisk, because it was a "new thing" and it was "free". Now they're looking into Nortel's BCM system instead.
The only system I've ever installed as "pure IP" was a very small 5-user Talkswitch installation. There was 1 analog line completely separate from the system used by a faxmodem. Far as I know, it's been working fine, but also I had to do a lot of research regarding the service providers and their QOS setup (For serious installations the provider should offer DiffServ).
Be prepared to do some reading.
Perry
