[tesseract]

It could of course just be a coincidence... however I am reminded of the story about how the (new) Mini Cooper exhaust tip was modeled on the bottom of an aluminum beverage can, because the designer happened to find one lying around when building a mockup, and afterwards no one saw any reason to change it. Maybe a designer traced their iPhone while working on an early sketch of the laptop, and then the detail just stuck?

[mitjak]

But, the unibody MacBook design came well before iPhone 4?

[tesseract]

The MacBook in question is the October 2010 redesign of the Air. It's conceivable that there were iPhone 4s (or prototypes of such) in the Apple design office at the time it was being designed.

[jbrennan]

Then maybe the contour of the iPhone 4 was designed after the groove on the MacBook.