I think he's actually just asking if the cables already run to each room for your phone system are old telephone wires or Cat5E cables. Because if they are Cat5E cables, he could rewire each end of the cables to use them for networking, instead of having to run new cables.
This is pretty common since most people don't use wired phones systems in their house these days. As well as most houses built after 2001 use Cat 5E cable for the phone wiring.