Justin M is correct. RJ11 ends will work in RJ 45 inputs. Cabling is not an issue. Ip phones are easier to move if needed, but a patch panel solution for digital is just as easy. If you are set on IP then we have done fairly big installs with ESI phones and there is no big difference in the functionality of the phones. As far as seperate networks, I do not no if this is possible if you will be using VIP. If so then the local computer has to be able to contanct the ESI server.