[TELECOM Digest Editor's Note: The two extra pins are superflous when
> you have only one phone line; but the catch is _which_ two pins are
> missing. I can only speak about USA-style phones here, but normally,
> the first and fourth pins are used for line 2, while pins two and
> three are used for line 1 on USA installations. The easiest solution
> might be to get a second RJ14 for the splitter's socket, and make it
> identical to the downstairs arrangement. PAT]
Picking up on Pat's suggestion: Suppose the wrong pair is connected. ADSL signals are radio-frequency and will couple capacitively from one wire to the next, without a direct electrical connection. That's why, if you have a 2-pair cable, you can probably get away with connecting ADSL to one pair and the telephone line to the other. I haven't tried it, but in theory, it should work.