Many of us here do not recommend using the carrier supplied email address for the following reasons:
1. It is totally unfiltered so if it gets out and is "harvested", you will get more SPAM that you care to have with no way to filter it to a SPAM file.
2. You cannot that the address with you when and if you change carriers. Once you cancel the BIS account, it is gone.
3. The only way to read email to that account is on the BB itself. So in the event of a data outage (and they do occur from time to time) you cannot send or receive email at all.