Offsite Linkup to Cisco Call Manager - Possible?

We have off-site sales from time to time. I use a Linux box with 2 NICs in it as a gateway device; the VPN software runs on the Linux box so all the computers have access to the company network without each needing a separate VPN tunnel. The connection to the wireless broadband ISP we get for these sales also requires authentication; this box provides this transparently to the users. It also has a firewall, which protects the machines in use at the sale. This has worked perfectly for the past several years - I go out the day before and plug everything in right, test it, and then all they need to do is turn everything on each morning and follow the on-screen instructions.

At the main building, we have a Cisco Call Manager 4.2 box running the phone system throughout the building with a voice T1 interface to the PSTN. We run a mix of Cisco 7912, 7940, and 7960 phones. The CCM server and phone system was put in and is maintained by a 3rd party company. I have administrative access to the CCM, but not any of the routers/switches.

I had an idea that I believe should work, but wanted to post and see what more knowledgeable people think before delving into it too deeply. I’d like to get a few IP phones and have them linked to the main building so that somebody at one location can dial a 4-digit extension and reach somebody at the other. Also, I’d like to have the people at the sale be able to dial an external number utilizing the T1 line at our main building. Is this something that would be possible?

The wireless connection is 3.0 meg down by 768 k up - I would think that this should be plenty to support a few phones. I’ve poked around and discovered that one can re-program a 7912/7960 to work with SIP/Asterisk. Is this process reversible? Should I invest in a few non-Cisco IP phones? I’ve also read that it’s possible to create a H323 bridge between Asterisk and CCM. Does doing this involve anything complex on the CCM?

Finally, how difficult/complex is setting up something as described likely to be? While I’m not a total noob when it comes to IPT, I’m nowhere near comfortable with it and have never set up a system myself. I’m fairly fluent in Linux/Unix, though I wouldn’t consider myself an expert in them either.

Thanks in advance for any replies. If I can get something like this functional and have it working at our next tent sale, I think my boss would flip! :smiley:

1)AFAIK you can flash the firmware on the cisco phones to work with SIP so you won’t need to get new phones. I would try using soft phones with G729 first to see if it would work. You may have an issue using WiFi since the latency may be high.

Asterisk can fully support what you need. Good luck.