Apple released version 4 of their iPhone OS iDevice (iPhone, iPod Touch, iPad) OS last month after a grand WWDC unveiling. Although there are many changes and new features, not all are as obvious and noteworthy as multitasking, home screen folders, and background audio. After working with iOS 4 on an iPhone 3GS and iPhone 4 for a month, I thought I might highlight my favorite hidden features. Did you know these existed?