Trixbox and a PRI and wtf is that. Well here is some info on Trixbox
http://www.trixbox.org/ which is an IP PBX.
What is a PRI? This a digital circuit riding on a T-1 using 23 B channels and 1 D channel. So what does that mean, you get 23 digital phone lines. You can also add DID or direct inward Dial Numbers to the PRI to assign to phones on Trixbox. Google what is a PRI for more info. Here I would say that you could also add SIP lines to the system as well for cost savings. What is a SIP line? Well look into carriers like TeleSIP or Vitelity who can provide a virtual PRI an much lower costs and of course you would have to balance cost vs performance. Most of the the IP carriers tell you if they support Asterisk, which is what Trixbox is built on and give setup examples. This also solves the issue of not having to deal with the local telco.