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.
"That's it then. Cancel the kitchen scraps for lepers and orphans, no more merciful beheadings... and call off Christmas."