iPhone OS or iOS 4.0 is just released to the public. You can upgrade your 3rd generation iPhone or newer generation OS 3 to OS 4.0 to test the latest OS from Apple. The latest OS 4.0 support up to 7 simultaneous applications running at the background. Applications running at the background support these features:- Background audio, Voice over IP, Background location, Push notifications, Local notifications, Task finishing and Fast app switching.

There are concern about the battery life would suffer greatly when you are running many background applications. That will only happens if you turn on the push notification option and all the background applications are utilizing this push alerts feature. I guess you will need to prepare the charger at everywhere you go before the battery runs out.

The total download size of iOS 4.0 is 378MB. It is huge size and it would require a certain amount of time to download if your connection is slow. I downloaded in 3 hours with my slow broadband connection. Download and update to iOS 4.0 with your latest version of iTune software now. The home screen background is just amazing!