iOS 4 (previously iPhone OS 4, iPhone 4.0) continues Apple's relentless yearly mobile OS beta and release cycle. If 2007 was the mainstreaming of the multitouch user interface, 2008 all about the app store, and 2009 filling in the feature list, then iPhone 4 promises to be... well, that's why we're here.
(And yes, iOS. That's the new name Apple has licensed from trademark holders Cisco to represent the iPhone, iPad, and iPod touch -- and maybe soon Apple TV and who knows what else -- family.)
Apple promises 7 "tent-pole" features and 100+ new user features overall, along with 1500 major new APIs for developers. We're going to walk through the ones that matter most. As with previous years, Apple is likely to release a half-dozen or more betas, as often as every second week or so, leading up to a Gold Master (GM) seed on or around WWDC 2010 (date yet to be announced) for iPhone and iPod touch, and September for iPad.
Things can and will change. Features will come and go. And all sorts of iOS secrets will be discovered deep inside the code strings. We'll update when any of that happens.