Yes, the BlackBerry data plan is what gives you internet and email, and is through your mobile carrier, Cellular South.
Mobile carriers typically have internet or data plans for other phones besides BlackBerrys, but they are not the same as a BlackBerry data plan.
I'd suggest you read though the BlackBerryFAQ here. That will help things make more sense.
BlackBerry FAQ - BlackBerryFAQ
Also there should be a help section on your device with all the basics for using the phone.