More specifically:

A recall is a highly publicized affair, where the auto manufacturer sends out letters to all owners, telling them to bring their car in to be fixed for free.

A service bulletin is an item that will be fixed for free, but it is not publicized. The owner only gets the free repair if the fault happens to be discovered for other reasons.

At least that's been my experience. I've never had to pay for a service bulletin item. I guess what's being said in this thread is that sometimes service bulletin items are chargeable. My point is that the biggest difference between recalls and service bulletins is that with the former, they go out of their way to tell you the car needs the repair. With the latter, you've got to bring your car in of your own free will.