Also worth noting that non-app solutions do exist. [NextBus](http://www.nextbus.com/), for instance, includes both a web interface and an SMS-based query centered around texting it your stop number.
aside from word of mouth, or searching google for "metra iphone", i have no way of directing traffic to it like i would if it were a dedicated app in the app store/android market. i've often thought about just taping up flyers at each metra stop to advertise for the site.