IPhone and iPod touch applications will not be able to run in the background. This is what is learned from the documentation that accompanies the release of the SDK.
'Only one application at a time – reads the Apple's Human Interface Guidelines for iPhone – can run on the iPhone and third-party applications can never turn the backgrounds. This means that when the user switches to another application, answers the phone or checks their email, the application they are using closes. "
The reason for the choice of Apple intuitive. Apple does not want to clog the (reduced) memory of the device by adding active applications; above all, he does not want the processor to undergo an unnecessary load, making the experience of using the phone unpleasant. Translated into practical terms, this also means some limitations in particular for those applications that need to always remain connected to the network, for example an instant messaging program, or those that must operate constantly, such as a GPS, to be efficient. .
From some comments posted on specialized forums and the Internet it is also learned that you can easily get around this limitation which has no technical reasons, but opportunities. Apple, at this point, may allow some developers to get around the deal. All the others, if they wanted to do so, could be blocked from distributing software via the App Store since each application must be certified (and digitally signed) to be run on the iPhone.
In this regard, it is interesting to note that even Java, according to the agreements that the developers must sign, would not be entitled to run on the iPhone, since, as Macrumors notes, the documentation prohibits an application from launching other executable code, which then exactly that that Java does. It is unclear whether Sun had some go-ahead from Apple. Macrumors rightly points out that not even a PC emulator could be a feasible hypothesis at this point since it would be an "application" that launches other executable code.