I just noticed that the AT&T phone numbers are showing a 1 in front of the phone numbers on the BES example: 1515-555-5555 We have 1300 users with numerous carriers, but AT&T users are the only ones with the 1 preceding their number. When I inquired with our AT&T rep I was told it was a setting on the BES. Is anyone familiar with this and have an explanation for it?

I'm pretty sure it's not - you can change it on the phone and it reflects it in the BES Database.

It's not a BES thing. It's an AT&T SIM provisioning thing.