Yeah that’s right, according to the official Iphone Human Interface Guidelines that was published by Apple recently; only one application can be run on the iPhone at any given time. No applications running in the background, which means your iPhone is multi-touch, but not multitasking.
This should give the developers something to think about, a bit of a challenge, as if you are using an application and receive an incoming call you stand to lose everything for the previous application. Therefore, developers will need to develop a way to prevent data loss in such cases. Occasionally the quick-save option will work. If this is indeed the case maybe developers should be working round the clock to sort this problem out, as who wants to lose data if a call arrives?
Source — cdrinfo