I think that the confusion was caused by my comment that it doesn't make sense to use DID anymore. What I intended to imply was that it doesn't make sense to use stand-alone DID 'trunks' that are dedicated for this purpose only. That's the understanding that I got from the original post.

Yes, my company has DID service delivered via a PRI in my office. PRI channels allow DID calls to arrive over the same circuit that an outgoing call might use (commonly referred to as "both way" trunks, although technically a misnomer).

It all depends upon what's needed of the PRI at the time and what trunks are available. That's what is nice about PRIs: Traffic dictates how trunks are managed (automatically) instead of a fixed "incoming-outgoing" structure that would be set up with standard trunks. PRI trunks change their purpose (direction) on a per-call basis.

With 23 channels on a standard PRI available, any one of them can handle an outgoing call OR an incoming call to a DID number. It's referred to as "call by call" service. The constant handshaking process that goes on between the phone system and the serving CO determines how each trunk's purpose is determined for each call.

To delve more deeply: The 24th channel of a T1 circuit that's delivering a PRI (the "D" channel), communicates between the CO and the phone system. It's sort of a "modem line" between them, so to speak. This is to determine what's expected of the other 23 channels ("B" channels). The B channels will individually process calls however they are told via information exchanged over the "D" channel. This occurs on a real-time basis.

Oh, and for all intensive purposes: ALL incoming calls to PRI trunks are effectively DID calls. It's up to the end-user's system installer to determine where these calls are routed.

Ed Vaughn, MBSWWYPBX