I'm creating an app which connects to server and sends some text. If network (both wifi or 3g) is there, it will immediately send the text to server. But if there is no network, it keeps on polling for server connection every 5 minutes. All this part is working fine.

But when using iPhone 4 device, i want the app to check for server connection even when app goes into background. So, when app goes to background and when network comes back, it must be able to send the text to server.

How can I achieve it? I've seen some apps where they say that the app will upload photos to server even in background. How will they do it?