Do all of the phones that work on this system only need 1 pair?

If your using dkt digital sets yes
If you have ekt sets no its 2 pair
S/l sets 1 pair

There was something about the second pair to digital sets that i dont remember ,but never used them ever.

Yes, but...

Some instructions for add on modules (2020ADM, 3020 ADM) say you need two pair. That would be for the power that is on the unused pair following the functional pair.

Pair 1 would have the phone ext. 200, pair 2 would have 24 volts dc for extra power, pair 3 would have the phone extension 201, pair 4 would have 24 volts dc for extra power,etc.

It has been my experience that the second pair for power is never needed no matter what the instructions say.

If you were running a VERY long distance, you might use the second pair but I have never run any that far away to need the extra power.

OK thanks. Cabling a warehouse where a dk 424 is going to be installed. We'll just terminate two pairs to be safe.