iPhone OS 4.0: Out of the closet on 8 April

The iPad hasn't even dropped on UK shores yet -- expect it by the end of the month -- but Apple is already on to the next big thing, iPhone OS 4.0.

The company has announced an event on 8 April, which will offer a 'sneak peek' at the operating system that will power the successor to the iPhone 3GS. Engadget reports the iPhone eye-opener will take place at Apple's Infinite Loop campus in Cupertino, California.

Rumours abound about what we can expect from the latest version of the iPhone's software, pointing at multitasking and and better contact syncing with social networks such as Facebook. 

We should also find out whether you'll get a free upgrade if you have the iPhone 3GS, older models like the iPhone 3G, and the iPod touch. iPhone OS 3.0 was gratis for iPhones this time last year, giving many of the iPhone 3GS's new features to older iPhones for free. iPod touch users had to fork out a tenner for the update.

iPhone OS 3.0 gave us the heady highs of cutting and pasting, stereo Bluetooth and MMS messaging. What would version 4.0 have to do to give you the same rush? Let us know what features you'd like to see, in the comments.