I have a single cat5e cable to upstairs and would like to connect an rj11 jack for phone use and an rj45 for network use. It looks like cat3 only has 4 active pins while a single phone line only has 2 active pins. Since there are 8 wires in Cat5e cable this seems possible - appreciate any thoughts.
In theory it should be possible, but a few caveats, one, you will never get speed over 100mb for the data side, and there is a theoretical risk to the ethernet devices due to phone ringer interference. The link below talks about it and gives the correct pinout info.
Why not ask around for a VoIP phone? It will cost less than a landline and it will use the same link as the net, with no tricks about splitting the cable. Besides, a 'phone ring' signal is some 50 or 60V so if the cable gets damaged or you make a mistake in the wiring, you could burn your network card and switch.
