Following on Daring Fireball's suggestion that iPhone 4.0 might bring the Calculator, Clock, Stocks, Weather, and Voice Memo to the iPad, The Loop Insight argues that it might just be iPhone 4.1 instead:
Phone OS 4.0 will include lots of new features, just like you would expect to see from Apple. However, It doesn’t make sense for Apple to unify the two operating systems for 4.0 with the timeline they are working with.
Rather, I expect Apple to release OS 4.1 in September or October. It will not only address issues with the 4.0 release, but also unify the operating systems.
iPhone 4.0 would presumably hit with the 4th generation iPhone (not to be confused with an iPhone 4G for LTE which is likely 2012). For the last two years, new iPhone software has been released as beta at SDK preview events in March while new iPhone hardware has been debuted at WWDC in June. New iPod touch hardware has followed in September, typically with updated software.
If Apple sticks to this pattern, the above does indeed make sense as getting as many users -- iPhone, iPad, and iPod touch alike -- on the same version of the OS is better for Apple, better for developers, and better for users.
For us, we'll take it one step at a time and wait for that iPhone 4.0 sneak preview...