Yup. With BlackBerrys there is no way around having a genuine BlackBerry
data plan to get MMS, email, BB Messenger, etc. Unlike regular cellphones, BlackBerrys rely on a partnership between the carrier, RIM, and the device.
Maybe check out: How to use BlackBerry on Generic Data Plan - BlackBerryFAQ
It might illustrate the differences of what you can do on a legit BB data plan vs. a basic carrier (generic) plan.