My last job was an AT&T ISDN Centrex job for a NYC agency. Maybe 3500 stations, as I recall. We had a "butt set" that could emulate am ISDN digital phone. It was a little clunky, but you could plug it into the demarc and dialing a few combinations of numbers, pull dial tone - if the circuit was good from the co.
ISDN was different in that it was 1 pair from the CO and then it fed into local equipment on the floor and then came out as a digital set using 3 pair (Voice, Data, Power). If the service was bad from the CO, it was easier to use the butt set to prove the trouble.
I heard they went VOIP 4-5 years ago.
Sam
Last edited by Silversam; 01/08/17 07:41 AM.
