Someone's created a new iPhone app with straphangers in mind. It's called MetroCost and it "can help you determine how much money you're saving (or losing) with an Unlimited Ride versus a Pay-Per-Ride MetroCard. All you need to do is swipe across the (picture of a) magnetic strip each time you ride, and MetroCost will do all the math for you." Now, can we get one that tells you when the MTA keeps the change?