The reason I ask is that it ends in vzw.blackberry.net
My gut says no for that exact reason. I'm pretty sure you can keep the same user name (i.e. user@) but the subdomain will change (i.e. from vwz. to att.)
Cannot have the same blackberry email when switching carriers. The one you have now is tied to VZW and when you switch your BIS will be tied to ATT. If would be like saying if you switched from Comcast to Verzion Internet service.... could you still have your comcast email. Not without a comcast account.