Hey Jason,
I did one of these recently, and I'm assuming the voice side is a voice PRI, like the one I did. I was skeptical of the idea at first, but it's actually pretty slick. One caveat I rememeber is, you'll want to make sure the provider gives you the flexibilty to work with you on the channels they hand you. I cound't get it to work without making sure the voice channels were the back end of the timeslots - i.e., the last channel of what will be your PRI group will in fact be the D-channel at 24.
Here's the important parts of the config:
controller T1 0/0/0
framing esf
linecode b8zs
channel-group 0 timeslots 1-8 speed 64
pri-group timeslots 16-24
In doing this, you create yourself one serial IP interface via the channel-group command and a separate interface which is the voice PRI via pri-group. They'll look something like this:
interface Serial0/0/0:0
ip address 192.168.1.1 255.255.255.240
ip access-group 110 in
ip nat outside
ip virtual-reassembly
!
interface Serial0/0/0:23
no ip address
isdn switch-type primary-ni
isdn incoming-voice voice
no cdp enable
Hope this is helpful, and good luck!
Jerry Craven