iphone programming objective-c : track user location in background questions

i have read that we can track user location in background. I have put in plist backgroundmodes array = location. I want to know if this only work with iphone 4 and 3gs? Also , when the user change location while in background, does it triggle the DidFindPlacemark method?

fin开发者_StackOverflow社区ally is there a tutorial with "CODE" somewhere or a sample for this thing?

thanks

I think you're looking for CLLocationManager, which is the GPS implementation. It has no UI and runs in the background, but you don't invoke it from the PList, you implement a class. Find the "LocateMe" example project for the code. This works in iPhone 3 on iOS 3.1.3, that's as far back as I have used it.