You can't convert a RJ45 signal to RJ11, one is a digital signal, the other is analog, and both use totally different signaling methods and protocols. Now you CAN use an RJ45 cable with the right wires hooked up to transfer a phone signal if that is what you are asking. Usually you see similar connectors on ISDN modems, I think those are 6-pin though.
Maybe you need to re-word what you are trying to do here.
As far as the wire diagrams http://en.wikipedia.org/wiki/Ethernet_over_twisted_pair