Just finished my first app. Its a truck starter app, since I have that GSM relay wired to my truck starter. All the app does is call the trucks phone number, and then disconnects after about 10 seconds. By that point, the truck will have started.
My plan is to expand it such that the user can control any of the relays on the device, and also retain state (i.e. keep track of which relays are in which position), as well as being able to query signal strength, change your password, and add phone numbers to the white list.
It'll be interesting to see how it goes...eventually I'd probably like to create profile within the app, allowing the user to switch between different devices that they want to control. I haven't really investigated whether I can sell it on the market, as it makes use of private API's (ITelephony). Does anyone know if you just need to have the code packaged with your app, or is there a general restriction from having that level of control over someones phone?