If you are buying the Blackberry to use for mail, you will need the Blackberry plan.
If you are not on a BES, then you will use the web client (like me).
I set up my local ISP, Yahoo, and other accounts by logging into the Web Client page. It is quite simple once you set it up.
Here is the web client page link: https://webclient.blackberry.net/Web...ite=mycingular