Most carriers allow us to get away with sending whatever we want for the calling party number. It's a great thing for those of us tweaking the rules to allow "tail end hop off" and send the CPN from a caller in another LATA/state/etc.... However the US law states that the carrier is supposed to only allow us to send numbers that are in the range of DIDs on the span and in the absence of a number being sent they insert the BTN. If you're placing calls out over an LD (Class 3) circuit than the calling party number sent could be a toll free or something you requested be sent (or the person taking the order forgot to ask you and maybe nothing is sent).

But for Local (Class 5) type circuits regardless of the type; CAS/PRI/E&M/POTS some carriers force the BTN. Others allow you to send any of the DID's you ordered with it, and many still allow you to send whatever you want regardless of whether it's even a correctly formatted number.

I have personally seen the variations and found that most legacy verizon LECs are tight and AT&T Local, MCI local (now verizon business local) are more flexible. regardless of the switch types; EWSD, AXE, 5ESS, DMS100, 250, 500 and so on.

Since you're taking about an E1 I'm not sure where you are but your carrier is inserting the number. talk to the SE on your account and request a change; explain that you want to make outbound calls but have the call backs be sent to a call center.

Good luck/

->N