This has been a long running problem. We use the 3COM NBX v3000. We also use the Desktop Call Assistant (actually, because of this problem with the TSP, I've written my own version of the Call Assistant that will still display a directory even if communication with the server is down).
We initially installed the TSP and DCA on everyones PC. After a while we noticed a pattern. The TSP would crash, brining down many vital services with it. After months of trying different solutions, none of which worked, we built a bare bones w2k3 server and installed the TSP on there using Microsofts remote TAPI client/server architecture. This works pretty well, but the TSP sometimes quits working, making us uninstall and reinstall.
This server doesn't have any anti-virus or other software. It is simply W2k3 with the tsp installed.
Right now, I am just looking for anyone else who uses 3coms TSP. Whether it works for you or not. Thanks in advance!