I had the same problem with the early TIVO units, where the modem would lock up.
If your client has a PBX system do not punch the CO off the phone system, punch it down before the KSU at the network interface.
Also, if your client has ISDN or DSL service in the house you will need to install DSL filters to all the DSS units, 2 wire and others make these, about $9.00 each.
Finally, check to see if the client's personal computer is punched down onm the same line, sometimes dial up modems can interfere with ech other and cause lock ups.

Good luck!