Merlin Mann started up a discussion for iPhone app ideas and the floodgates opened.
I’d love to have a GPS- and Bluetooth-enabled phone settings app that would tell the iPhone to activate/disactivate call forwarding based on your location. For example, if you get poor or no signal where you live, you could pair the app with your home computer and every time you come home it would tell the iPhone to forward calls to your home phone.
Technically, I’m not sure this type of app would even work. First, there is very little (if any) documentation about the iPhone’s Bluetooth capabilities in the SDK. Second, even if hooks were provided, I think the app would have to be launched in order to perform any sort of action (such as setting call forwarding); which sort of defeats the purpose.
Anyway, some of the ideas in the comments on Merlin’s article are great. Take a look. Especially if you’re a developer.