Although both T1 and PRI use the same low-level signaling (i.e., ESF/B8ZS), that's pretty much where the similarity stops.
ISDN uses a control language over the assigned "D" channel to handle the coordination of the traffic over the remaining 23 "B" (Bearer) channels.
If you do a "DEBUG ISDN Q921" you'll see the layer two ISDN managment traffic: if you do a "DEBUG ISDN Q931" command, you'll see the layer 3 ISDN management traffic (call setup, call progression, call ending) ... the ISDN L2/L3 is not part of the Ethernet & TCP/IP L2/L3 ... consider it a sub-layer.
A T1 at the same level, does not have that kind of coordinating protocol. A T1 (channelized) usually relay on a few "robbed bits" (RBS - "Robbed Bit Signaling" Also CAS - "Channel Associated Signaling") to indicate phone off-hook, inbound ring, and perhaps some other info, depending on the endpoint systems.
For a pure data application, the T1 bandwidth is unchannelized and is pretty much a raw bit stream used with an encapsulation like HDLC, PPP, or Frame-Relay.
To use more than one channel on a PRI for data, the channels must be aggregated using protocols like BONDING or MLPPP.
Here's a link to isco's Internetworking Guide online:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/index.htm
It does a pretty good job of covering the high-level details on all of the technologies and protocols.
Good Luck
Scott
