The multi-tasking ability in iPhone OS 4 allows faster to switch between apps back-and forth and provides developers with seven new multi-tasking services available. These include, background audio, and so that VoIP Apps contrary can take VoIP calls even if your iPhone is in sleep mode or user who has run a different app. According to Apple, the iPhone registered with multitasking OS 4, despite no significant loss of performance or excessive battery power.
Following is the video preview of iPhone multitasking live in action.