I don't think you can cancel the data plan on Sprint.
To the OP, if those things don't work, go to the Email Setup icon on the device and log in. If you don't have the information needed to log in, call Sprint Customer Support and have them reset it for you.
Then click on Email Accounts and for EACH email address click on Delete. Confirm that you want to delete that account. Repeat as needed.
Alternately, if you just don't want the phone to alert you when you get email on the device, go to the Profiles icon, scroll Advanced ..., then scroll to the Active Profile, press Menu and select Edit. Then scroll to each email account and change the alert settings to NONE for both In Holster and Out of Holster.
Alternately, if you are just looking to filter SPAM, you can log in to your carrier's BIS (BlackBerry Internet Service
) from a computer and create FILTERS to filter out some of the messages.