I currently have both an IAD2421 owned and managed by XO Communication and a Cisco 2821. I am going to be upgrading to the PRI package that XO offers and they claim that I will need to get a "card" for my router. That is all they can tell me. The IAD will have a T1 (PBX) Digital Voice Port. This is where I will grab the PRI services off of into the 2821 if I can ever figure out what kind of card I need to get. I will have 17 channels (or trunks) and the 2821 will not be doing any Internet data services at all just VoIP services for CallManager.
Since no one can seem to answer this question I have given 500 points to the person that has the answer. Many thanks!