Which applications launch into background state?

I'm reading through the multitasking documentation开发者_开发问答, and it has a few references to apps which launch directly into the background state, never entering the foreground state. Is this really allowed for regular apps? Can anyone give me an example of an app like this?

VoIP apps are the biggest one to use this feature. Basically a VoIP app can register itself with the system to be notified when network traffic is intended for it at which point the app takes over handling the incoming traffic (i.e. receiving a call). Skype and Viber both use it.

From the iOS Developer Library (emphasis mine):

Including the voip value in the UIBackgroundModes key lets the system know that it should allow the application to run in the background as needed to manage its network sockets. An application with this key is also relaunched in the background immediately after system boot to ensure that the VoIP services are always available.

The significant location changes backgrounding service also allows an app to be updated with the new location even if it's not running.

Other than those two cases, an app can't do anything from a terminated state until the user launches it.

When you use location manager with significantchange notification, App gets backgrounded automatically if the app is killed, when there is a location event