An advertisement banner for doubleTwist—a software application that lets users access their iTunes library on any device—has shown up on a display window directly next to the San Francisco Apple store's main entrance.

If you're wondering how Apple allowed this to happen, the window technically belongs to BART—a Bay Area's transit system—and because the advertiser, DVD Jon, had purchased that specific ad space directly from BART, it's perfectly legal and there's not much that can be done about the "Cure for iPhone Envy" product placement. I'm curious to see what kind of marketing magic, if any, Apple's going to create ...

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