Fast ethernet (100baseTX) uses the same two pairs as 10baseT. It most definitely doesn't use all 4 pairs. If it did, then it would be pretty miraculous how I've been running 100baseTX all these years without connecting two pairs.
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You can check documentation all over the place, including CISCO to verify this.
My first guess regarding Roger's problem would be bad connections, not broken wires. I have always used solid core wire and have used both a punch-down tool as well screw-down wall terminals (which is what I'm using right now).
When putting in a new wall plate at a friend's house we ran into a similar problem. The replacement plate was not like the original. It was meant to have all the pairs wired IN ORDER. ie. you didn't skip pin 4 and 5 when wiring the TX lines. This was a bang-your-head-on-the-wall scenario once we found out.
Continuity testers are nice, but if you don't have access to one, you can also isolate the problem by using different runs of known-good patch cord, skipping various connecting segments as you isolate.
Bottom line: I would check the wiring requirements of the wall plates.
And for good measure: standard is: 1 & 2 are RX (+ and -) and 3 & 6 are TX (+ and -)
Bruno