> It sounds like you would never need more than two wires, one in each direction, but if you used different frequencies for telephone, computer, fax, etc., you could use them all on the same two wires.

Not if it's copper. Copper won't reliably transmit signals of all frequencies -- in fact, its bandwidth is pretty narrow. Actually it is highly likely that, in the far future, we'll only have ONE fiber optic wire coming to each household, and absolutely everything, in and out, will be done on that one wire. Fiber certainly has enough bandwidth to handle pretty much any current household need. Although that may not be such a good measure, as needs tend to increase along with technological capacity.

The other advantage to fiber is that you can have a single wire go a very long distance without the need for it to be amplified. It's not reliable to have a segment of copper wire longer than 100 meters -- beyond that, the signal becomes too weak to be reliable. You can slap a repeater in, which serves basically as an amplifier, but if you're going a long distance, that gets old quick. Copper's latency is also not admirable. A signal travelling through copper wire won't travel as quickly as a signal going through fiber. Latency isn't so important when talking on the phone or watching cable TV, but it's a big deal with computer networks, because the timing algorithms in the various networking protocols use the knowledge of how long it takes for signals to propagate through the wire to learn about the state of things out there on the network. I've probably lost you by now, but these are some of the things you have to take into account when analyzing how your house is wired up. In case you're wondering why I know any of this, I work for a computer networking company. :-)