I had an install in a hotel a few years back for a franchise that required two line phones in every room. The electrical contractor terminated all the in room wiring on 8P/8C jacks using 568B. Connecting the second line, we had to connect the jumpers onto the green pair (typically line three). Yes, USOC is needed if using three or four line analog phones or you would be splitting the pairs.
Auto sensing network equipment doesn't do anything with a cable run terminated A with a B patch cord (or vice versa) Use a cable tester and and test from an A patch cord to a cable run terminated A and a B patch cable at the remote end, it will show as a straight thru cable run. Now remove the B patch cord and replace with a crossover cable (one end A, other end B) and you'll see the orange and green pairs flipped - this is where the auto-sensing kicks in. Before auto-sensing, had to use cross over cables when connecting switch to switch, etc.
Computers will work on two pairs if needed. They only use pins 1, 2, 3 and 6. Now granted, it's not ideal and will definitely fail any cable test and not recommended but have done it in situations where there is one cable run and customer wants a phone and computer and running a second cable is not an option.
I don't specifically order A or B patch cords, I order the length and colour I need and use whatever I receive. Trust me, the A patch cords are computer patch cords - Cat 5E and Cat 6 rated.
