I’m working on a location based app, which needs to send coordinates to server at a defined interval. It works properly on iPhone 4, even in background(see: iOS HTTP request while in background).
A friend of mine installed it on iPhone 3G with iOS 4.2.1 and after he put the app in background, it was killed by the OS. The app has 3 screens, first is a login screen. After he returns in foreground, the login screen appears again, instead the screen he has left open(which means the app was killed and restarted upon re-launch). on iPhone 4 work as expected.
Why on iPhone 3G the app is not run in background even it is declared as location app(“required background modes” is set on “app registers for location updates”)?
Because on iPhone 3G, multitasking is not officially available.
(you can jailbreak the iPhone, do some plist hackery and make your iPhone 3G have multitasking, but I suppose you don’t consider jailbreaking at all even if you know about it.)