On the blackberry, you could do something called, "delete previous".  For those of us who get hundreds of e-mails a day, we only usually want to keep about a week of e-mails in our device at any given time and want to delete the remainder of them.  How do you keep 500 e-mails and delete the previous 500 without having to manually go in and check each one?  There HAS to be a way.

From the inbox, menu, delete.  Emails will have checkboxes next to them. Select the ones you want to delete.