said by kherr:[ There is also no reason to run Cat5 or 6 for voice. Just run a 4-wire flat cable. You aren't going to have any performance difference for phone conversations ]
Around here you have to use at least cat3 for phone. I thought that was national, but may not. It's my understanding that the usual 4 wire round cable (untwisted, red black green.yellow) was phased out years ago.
You use cat3 only if you want. Otherwise in your house you can use whatever you want.
You do realize that there are millions of homes using the old 2 pair non-twisted don't you? Their phones work. Also there are millions of miles of underground cable that has been in use for decades long before cat anything.
Why put that high dollar wiring in a home and feed it with the same old? You're never going to have anything better than what your source is.