The unreleased iPhone unit later resurfaced on Gizmodo, a popular gadget website, which promptly splashed photos and details of it all over the Web and touched off a storm of publicity and speculation in the technology blogosphere.
The device featured some noticeable improvements on the current generation model, including a front-facing camera for video chat and an improved version of its standard camera, among other goodies.
Apple has released a new iPhone for each of the past three summers. Although the company has not formally announced its plans for this year, it is widely expected to launch the fourth-generation model this summer.
There was plenty of online discussion on Monday about whether the device was the genuine article. But a consensus emerged among the bloggers who track Apple's every tic that it was, in fact, a next-generation iPhone prototype.
Then Apple, famously secretive and protective of its trade secrets, moved to get the device back.
Gizmodo late Monday posted a letter from Apple general counsel Bruce Sewell to Gizmodo editorial director Brian Lam. The letter said: "It has come to our attention that Gizmodo is currently in possession of a device that belongs to Apple."
The company asked that the iPhone be returned, and Gizmodo said it would do so.
Apple did not return a call seeking a comment.
According to Gizmodo, the iPhone was left in a bar in Redwood City, California, on March 18 by a young software engineer. The device was found on a stool by an unidentified person, the blog said.
Nick Denton, head of blog network Gawker Media, which owns Gizmodo, said in published reports that the site paid $5,000 for the iPhone prototype.