Everyone is designing a phone app these days, so if you want in on the action, here are a few of my ideas:
1) dog to Spanish translator;
2) body hair maintenance scheduler . . . it's a little stick figure and various areas light up when it's time to trim-- ear, nose, beard, nether regions, etcetera;
3) an alphabetic communicator, so that you can send a message of written words to a friend without having to speak, and then (perhaps) your friend could reply back to you with a written reply, and this would all appear on the phone screen . . . this one seems the most promising of my ideas.