A great thing about messenger apps is letting people know when you're away (even if you're not). Convenient, no? An Apple patent spotted by AppleInsider describes a feature that would let you do the same for voice calls, too. Since it's just a patent and (and thus, might never be developed), Cupertino doesn't have anything solid on how the system will work. The documents submitted to the trademark office do offer some ideas, though. For instance, it says the feature would upload data about its condition (such as its ringer volume, vibration status, device location, cellular strength, battery life, etc.) to a remote server.