4sqtransit is a foursquare app that tells you where the nearest transit station is and when the next train/bus/ferry/etc is scheduled.
All you have to do is go to the 4sqtransit site, select the transit agency in your city, log in using foursquare via their link, authorize the app and you’re done. 4sqtransit will then send you a text whenever you check-in to a venue within 100 of a transit stop.
One note: Make sure that you have a cell number associated with your foursquare profile. 4sqtransit only works if you have a number listed so it can send the text messages to your phone.