Originally Posted by fratts
You will have to log on to the BIS website (ask your provider for the link) and there will be a change device option, where it will ask you for your new PIN number and problably the MEID.
This would work if you changed devices on the same carrier. Since the OP is changing carriers as well, there will be a different site to log into.
Remove all of the email addresses from your previous BIS account. Create a new account on the new carrier's BIS site and set up your email addresses to be forwarded to your new device.