There's still a lot of stuff riding on 4-wire designs, and I, for one am happy that that's the case.

While most of T-1s and 56/64K circuits are designed as a single pair nowadays (distance permitting)it never seizes to amaze me how many old and not-so-old analog and tie lines are still around, most of them with separate T and R pairs.

A lot of folks love converting 4-wire circuits to 2-wire ones, whenever possible. I never do. Truth be told, I've done the exact opposite on many occasions.

While I don't have the mileage required to confidently state that two-pair designs are better, I will state that I do like them better.

My $0.02 only...

"...Time moves slowly and it goes so fast..."

(Sandy Denny)