In this tutorial I'll help you to understand why you don't need to pay for the more expensive wiring inside your building. Phone systems and computer networks are very different in terms of how they work and how they're designed. That's because the manufacturer's KNOW that people are going to re-use old cable that was in their building when they moved in.
Computer networks are almost the direct opposite.
As well, most networks have a limitation on the length of cable that is much shorter than phones. The bottom line on this one is simple, folks. Run CAT5 for your computer network and CAT3 or lower for your phones. Active Phone Server . Telephone Answering Machine Software for voice modems.