It is what telco's usually call a "dry-pair" or a "no-load pair". You only
need 1 pair (2 wires) with nothing on it. The key is that you don't want
the telco putting power on the line. If you want to use their PBX
connection I think you need 2 pairs instead of 1 though.
I just tested LRE yesterday and the setup is very easy. Assuming you have
pretty clean lines then you should have no problem getting it to work. The
2924 XL-LRE is even smart enough to reverse the wires if you get tip and
ring swapped.
Mike