OK. If you search the forum, you will find other discussions about this subject.
Basics you will need to know:
1. Use Display.setCurrent(null) to push your application into the background. Note that this is not strictly part of the MIDP standard, and will not work on all devices. However, it does seem to work on Series 60 (and some other) devices.
2. Older Series 60 devices push the app into the background when the red-key is pressed. However, this was changed in later versions, so that the red-key now terminates the app. You can force Series 60 devices back to the old behaviour by adding:
to the JAD.
3. Many actions, such as connecting to the network, are subject to security restrictions. Depending on the security settings (selected by the user in the device's Application Manager), the device will ask the user for permission before proceeding. Depending on device, it might be possible to disable these by signing the application with a trusted certificate (which will cost you money), but it also might not be possible.