I think your carrier can clarify this better, but from what I know once you have a basic BIS plan BBM is automatically an activated "feature" for BlackBerry smartphones..
Just to clarify a bit - BIS is a data plan. It stands for BlackBerry Internet Service. It's the BlackBerry data equivalent. Once a BB has BIS it's on a data plan.
Posted from my CrackBerry at wapforums.crackberry.com