Curly:
A lot of that same terminology (or at least the concepts) still apply in Asterisk, which is just an IP based phone PBX.
So, he's using his SIP provider (which he would normally just have a phone connect to on a one-to-one basis) as a Trunk. Think of it as like having a POTS line plugged into an old AT&T Merlin. He then has SIP stations (phones).
So, a SIP TRUNK would be able to have multiple phone numbers on it, pass DNIS digits, all that kind of stuff. So, in this situation, he doesn't exactly have a trunk; it won't do multiple calls, you can't have multiple numbers, stuff like that, although he's using his sip phone provider as a pseudo-trunk to make outbound calls.
He would have one channel for external calls.
Now, at work, I have an asterisk system, about 130 phones (SIP stations), two PRI's (46 trunks) plus a few SIP trunks. Then I have a IAX (Inter-Asterisk Exchange) over our internet provider to another asterisk system, which allows for dynamic connections between the two systems (I only have to do one IAX connection, but it will create as many channels as needed to handle the traffic). This allows us to call station to station between two different offices without using external trunks, or long distance charges.
Additionally, on my system here, I have 8 virtual fax modems, in a fax modem pool. This is really slick... since I have DID numbers pointed to the fax pool, I could even receive multiple faxes on the same number. Asterisk looks at the inbound number, receives the fax, then based on the inbound number routes the fax (converted to a PDF) to the appropriate department. We have about 15 different fax numbers, with 8 modems in a pool. Currently, we receive roughly 2000 pages a week in faxes.
Additionally additionally, everyone has a fax client on their PC. Using a virtual printer... so they just choose the fax as their print destination, a little popup comes up asking the number that they wish to fax to, the fax is queued up and sent out. As simple as printing, the users can fax.
We have call queues, pickup groups, group ringing, status (not only DND but Lunch, In A Meeting, etc.) all visible to the two touch-screen operator stations at the front desk.
Lots of stuff you can do with Asterisk... and if you couldn't tell, I'm pretty proud of the versatility as well as the stability of the system here.
Just my $.02
"What the captain doesn't realize is that we've secretly replaced his Dilithium Crystals with new Folger's Crystals."
--Greg