Does the following work? I have two phones in room A. I run a cord from Phone 1 and Phone 2 into a 2 line/1 line splitter. I then plug the splitter into a RJ45 patch panel. Cat5 8 wire cables run from that patch panel to a patch panel in Room B. I plug another 2 line/1 line RJ45 splitter into the patch panel, then run normal phone cables from the splitter to two phone outlets. Yes, I know there are better ways to do this, but this seems cheap and I have the parts (making it very cheap.)
While Cat5 won't provide any benefit over Cat3 for POTS, I would beg to differ on the statement that there's no benefit over "plain old wire." As one who has been involved in the installation of phone systems for over 30 years, I can tell you that POTS can absolutly benefit from CAT3 or better wire particularly if you live near a radio station's antenna or suffer from other crosstalk/interference problems. The greatest demonstration of this was a job I did at the Maui News about 20 years ago. For years they were plagued with having to listen to a local radio station in the background on every phonecall. No amount of grounding or filtering would eliminate the problem. When we installed CAT3 for their new phone system the lines were dead quiet. No more "music on calls" to put up with. I thought the editor was going to kiss me but fortunately he opted for a hardy handshake. As a test, before we put the new phone system in service, we tested the lines with just POTS and 2500 sets to demonstrate the benefit of the CAT3 cable and it was clean as a whistle. In another case, in my friend's home they always had a radio station in the background on the phones at the far end of the house. I replaced the old "quad" wire with a length of CAT5 and the lines are now quiet. Bottom line folks - CAT 5 is dirt cheap now. Use it (or better) for all phone and data runs. I even run it for doorbells so it can support intercom and video.