Gap has certainly been a good buddy to location-based mobile check-in services lately. Last week, the retailer formed a partnership with Facebook Places and sponsored a giveaway of a pair of free Gap jeans to the first users to check in at Gap stores (up to 10,000 pairs at locations across the U.S.) via Places. Gap also rewards users of Places' competitor Foursquare by advertising 25 percent discounts of Gap merchandise for Foursquare users who check into Gap store locations.

Now the co-founders of Foursquare, Dennis Crowley and Naveen Selvadurai, have found another way to work with the marketing team at Gap: by walking the catwalk. OK, perhaps they're not exactly walking the catwalk, but they are modeling its clothing in the retailer's latest ad campaign.

The new Gap campaign, which is running on television, in print and online, features a number of relatively high-profile people, including former First Niece Lauren Bush (Jeb's daughter), actor Ryan Kwanten from True Blood and style blogger Susie Bubble. It asks the question: “If you could give anything in the world, what would it be?” The ad campaign is charity-linked and the celebrity "models" are all sponsoring a different charity for their efforts.

For the charity part of their modeling gig campaign, Crowley and Selvadurai chose to benefit Camp Interactive, a charity that combines nature and technology to benefit inner-city youth.

If you're curious, you can check out some of the commercials from the campaign. For each of the “Likes” the video receives on Facebook, $1 will be donated to the charity featured in the video, on top of a base $150,000 donation from Gap. Customers will also receive a 30 percent discount on one regularly priced item from Gap.