Google Android Phone Codes

These launch a special intent type android.provider.Telephony.SECRET_CODE. You can define your own in your apps by registering the appropriate intent filter.

It's just a way to allow an action access without explicitly putting an icon in the launcher.

This website has a little more information on it: http://android.amberfog.com/?p=422 I imagine there are a lot more that could be discovered by scanning through the various manifest.xmls for the system apps.

Pretty interesting but just a note that these codes might not be same across versions and hence not to be tried on your current phone(Imagine resetting everything while trying to launch some test :)).