The Wall Street Journal reports that the Apple executive in charge of the iPhone has left the company following a string of stumbles with the device, and what sources said was a falling out with Chief Executive Steve Jobs. Mark Papermaster, Apple's senior vice president for mobile devices, has left the company, an Apple spokesman said Saturday, declining to provide further details. Papermaster had joined Apple just 15 months ago from IBM. Exactly how much part the problems with the iPhone 4 played in Papermaster's exit is unclear. Several people familiar with Papermaster's situation said his departure was driven by a broader cultural incompatibility. A spokesman said Papermaster's duties will be handled by Bob Mansfield, the company's senior vice president of computer engineering.