[Asterisk-Users] Connecting asterisk to existing PBX - newbie question

[Dan Reagan]

I have a question regarding interoperability between Asterisk and an 
Inter-Tel (I believe it's an Axxess) PBX at a client's location.

My clients currently have an Inter-Tel system that they're fairly happy 
with but they're being bludgeoned by Inter-Tel for their proprietary IP 
based phones. The phones themselves are on the order of $1,000 each 
(they're in a lease and only see the monthly charge when they add a new 
phone. That $1000 is a rough approximation on my part from the last 
lease addition which was $24/month with 42 months remaining).

I believe that many of the people that they have who are currently using 
the proprietary phones would be quite happy with a basic SIP phone (they 
don't need ACD login or other advanced features) however Inter-Tel's SIP 
gateway product is quite expensive. The sales person never actually gave 
me a real quote but said things like "pushing $10,000" and "very 
expensive" and "You don't really want it". My feeling was that they want 
to keep this client with their proprietary phones (and at $1000 each I 
can see why).

I think that I could craft a gateway of some sort out of an Asterisk box 
doing nothing but taking a handoff from the Inter-Tel PBX and passing it 
out to SIP phones attached to the Asterisk machine but I'm not 
absolutely certain how to go about it. Off the top of my head I see two 
rough directions to go but I'm somewhat out of my depth and would 
appreciate any insight, particularly with regard to the details <g>.

First, I could take an existing 'single line card' in the Inter-Tel 
system (8 FXS ports already installed in the existing PBX) and run that 
into 8 FXO ports on the Asterisk machine. I'm assuming that from there 
it would be a fairly straightforward to set up a 1 to 1 mapping of 
incoming FXO to connected SIP phones.

Second, I could take an existing T1 card (I'd have to buy an upgrade to 
get PRI functionality if required) and connect it to the Asterisk box. 
At first glance this seems to be a more flexible and better solution but 
I believe that on the Inter-Tel side I'd have some issues with mapping 
extensions to the outgoing PRI ports and/or extensions on the asterisk 
side and a fair amount of jiggling to get things working right.

Alternatively, would it be possible to just stick something like the 
AudioCodes MP108-FXO in the middle of the 8 FXS ports on the Inter-Tel 
PBX and some SIP phones? Initially I thought that this would work but 
further reading has led me to think that this wouldn't work and that's 
what led me back to Asterisk.

That's my very rough thinking. Any help would be greatly appreciated. 
Also, I'm sorry if this has been covered before on the list or 
elsewhere. I spent some time digging through the archives and couldn't 
find anything helpful but I'm sure that I wasn't perfectly thorough.

Dan Reagan