I see it like this:
The phone is unlocked (can be used on any network)
But the PIN is still associated with a BIS account, and therefore you would not be able to use Blackberry features without getting it released.

Or the person selling it doesnt really know what they are on about;
either way, you'd need a blackberry data plan, and until activated you won't know if the PIN is still associated to another account or not.