Originally Posted by penguin3107
The BlackBerry data plan allows your device to authenticate to the RIM infrastructure, which results in allowing you to use all of the data features that are native to the BlackBerry device. (Email, Web Browsing with BlackBerry Browser, BlackBerry Messenger, PIN, SMS and MMS messaging, etc...)
Without the BlackBerry Data Plan, you won't be able to use those features.
Actually SMS doesn't require a data plan at all. It is carried via the phone system, not data system, soo you need is a voice plan and SMS enabled. However it can get really expensive without an accompanying text plan.