I've built large systems with this but there seems to be nothing in the small TDM space for experimentation with TDM data on the telco network. I'll be working on a simple 1-4 DS1 version first starting with the framers and FPGA. If you are interested in working on this open source project drop me a line.
As of 04/02/2011 I'm planning on using the DS2155 framer to a basic plugin card. Eventually these will be plug in cards to add DS1's to the main FPGA/DSP board.