Pay Highway Tolls With Your Mobile

Personally, I thought the whole Good To Go! system they implemented on the new Tacoma Narrows bridge was pretty cool. However, that only works when you're driving your regular car. What if you're driving someone else's car?
While the Koreans have come up with a way to use your mobile phone to pay the toll, you still need to install a transponder in the car itself. Bah, I say. Why not find a way to just query the phone directly? There's gotta be a better way!
Via IntoMobile, textually.org