Steal this idea: Mobile public transportation planner

If I had an iPhone or Android-based phone instead my current piece of cellphone-shaped garbage, I would want this application: While walking someone, the user tells the application their intended destination ("I'm walking home now") and the application uses GPS information and a data connection to lookup public transportation alternatives to walking. It then suggests small detours or pauses in your journey (e.g. "Wait here, you're at a bus stop. When the #42 comes in ~2 minutes, get on.") which get you closer to your destination. As far as I know, this shouldn't be that hard to write and I'm surprised I haven't heard of it so far (of course, not owning a shiny phone, I don't follow all the apps written for them). It could also get more sophisticated by learning your pace or common routes and locations. In any event, this would be a useful tool and I think I'd take the bus more often if I had it.