Evidence of a major iPhone OS update surfaced yesterday as the folks at Boy Genius Report discovered traces of iPhone OS 4.0 in their server logs. This pairs nicely with the recent rumors of Apple's fourth-generation iPhone, which is supposedly in or entering production and could appear as early as mid-2010.
It's worth noting that the iPhone 3G/OS 2.0 and 3GS/OS 3.0 both arrived during the same period (July 2008 and June 2009). While few details are currently available, it seems fair to expect a major platform update and new device in the coming summer.
BGR also discovered iPhone OS 3.1.3 in the logs, which will probably bring minor bug fixes and tweaks to the present version 3.1.2, and should appear soon. Let's hear about all of the changes you'd like to see in the forthcoming iPhone hardware and software.