Damon Jebb wrote:
You should avoid mixing telephone and network wiring. Telephone wires carry anything upto about 50 volts DC which will fry anything that you connect it to on your computer (by mistake, but plan for it to happen!). Also, even though they are insulated the wires do communicate with each other because of the electro-magnetic field around them. Even in wires carrying a relatively low voltage this can be a problem, which is why the specification for Cat5 is so stringent compared with telephone cables. If you add the telephone voltages to the mix you will almost certainly cause you network problems, but you could also cause problems on the telephone that may affect the quality of dial-up internet access.
Ethernet (10 base T) was designed to work over existing phone wiring. The frequencies used by phones and ethernet are so far apart, that interference in either direction is unlikely. Also, the NICs are designed to safely handle a few hundred volts. Also, PoE (Power over Ethernet) places power directly on the pairs used by ethernet.