Jon,

I have about exhausted my ability to speak lucidly about phone wiring. I can look at it and recognize the parts, but can't speak too much about standards and protocols. We have four wires, as was noted above, but that's not because four are required. It has to do with different lines on one phone or in one room. Here what we call DSL comes on the regular phone line, but it has to do with the requency of the signal. It doesn't interefere with the regular phone service, dial tone, etc. I had started laying out the wiring for my phones when the DSL folks arrived. Since I had done all of that he could simply make the connection, so what I ended up with is a filter at the box outside (which the phone company needs to update, but I haven't gotten around to calling about that). This eliminates the need for a small filter on each phone. Idea being that it blocked any DSL interference on regular phones.

Here the outgoing signal is slower than incoming. Messages go out at about double the reglar modem would manage. And yes, the plugs are different sizes, from the DSL modem vs the regular phone modem.

Take a look at this site, one of them I used to plan out the design and layout of my phone system. An engineer friend confirmed the soundness of choices, and offered suggestions where needed.

SRS