Gregmac wrote on 3 Jun 2008:
Ethernet and analog phones can easily share the same wiring, assuming you use Cat5 or better for everything. Analog phones use the two center pins of an RJ45 connection (pins 4 and 5, or the blue wires), while standard ethernet uses pins 1, 2, 3, and 5 (orange and green). You should be careful running analog phone service on a line that is actually connected to an ethernet device however - although it shouldn't be a problem, there is no guarantee your manufacturer didn't do something silly that will cause the device to malfunction as soon as the phone rings and 80V AC is sent down the line.
In general, if you use a patch panel in your wiring closet, you can plug your ethernet jacks into either a switch, or analog phone service as required (and generally you do not run them both simultaneously down the same wire). An RJ11 phone plug will fit into an RJ45 jack with no issues. The nice part about using a patch panel is you can reassign jacks as necessary - if you need an analog line into a given room, then you just plug it in at the patch panel and you're good to go.
If you upgrade your phone system to use VoIP, then you are already set as you can easily convert jacks to ethernet by patching them into an ethernet switch. You can even maintain some of your older analog phones by using an analog terminal adapter in the wiring closet, and patching the analog lines to your jacks.
Going further with VoIP phones, it's very popular to power them with Power over ethernet (PoE) from your wiring closet. In this case, you have a PoE capable switch (or injector) connected to your patch panel or cabling, and generally plug it into a UPS to provide backup in case of power failure.
Note that when using PoE or Gigabit ethernet, you cannot share analog phone service on the same cable as ethernet as they both use all 4 pairs.