I would not suggest this. I am an FtOCC certified mofo, and administrated an Asterisk box with T1 and SIP trunking for years. I am a firm believer in getting as much crap/headache hosted outside of your building as possible. Make it someone else's problem to wait for Verizon to repair your T1 at 2AM. You're going to save time, money, and your sanity.

I switched our business to OnSIP a few years ago based on someone's suggestion on this BBS (Phoenix32?) and never looked back. I don't have to ever call Verizon to service a T1 again or deal with mind-numbing Caller ID issues. Get some Polycom phones, point them to boot.onsip.com and watch it just work. Take a look at the plan without per-seat fees. Looks like it's right up your alley.