"Adding payments unlocks a lot of experiences that's worthy of a whole new [version] number," Jawbone senior product manager Jason Donahue told us. "We're changing the way people have to think about their fitness and their lifestyle ... No longer do we have to go out for a run with a giant phone in our pocket."

While it doesn't make much sense for a company to announce an entirely new version of its flagship product when the latest device hasn't even hit shelves yet, the Up4 is still an interesting device. At this point, Prentice notes that it's only compatible with American Express consumer credit cards, not corporate or prepaid cards. If you have an Up4, you'll also see a link within the Up app to sign up for an AmEx card, if you don't already have one. You won't be able to track your purchases from the Up app though -- both companies want to maintain strict data privacy policies.

Of the two new health bands, the Up2 seems far more promising. It's somewhat affordable at $100, and it's pretty comfortable, based on my brief hands-on time with it. The Up4 is an interesting concept, but it seems like a tough sell to convince people to spend more money just to get mobile payments. And if you don't have an AmEx card, you're just out of luck.