The description under startMonitoringSignificantLocationUpdates at

http://developer.apple.com/library/ios/#documentation/CoreLo...

is the place to start, where they state "If you start this service and your application is subsequently terminated, the system automatically relaunches the application into the background if a new event arrives."

The other required piece of information is that when you reboot the phone, it triggers this event for all applications that have registered this service.

More info at: https://devforums.apple.com/message/307725

If you're further interested, downloading the SongMap sample code from Apple will let you test this functionality yourself.