Usability 
Transit Tracker was developed in house by Portland Oregon's TriMet transit agency. Here is a document (pdf) with which describes the project in considerable detail. Transit Tracker, which covers almost all of TriMet's close to 100 routes, has a WAP1 wml version and a PDA html version that is also usable on WAP2 phones. This is a very nicely implemented mobile site. TriMet's designers obviously were serious about creating a usable site. For one, instead of a long scrolling list of all the stops on a line, like NextBus and WebWatch, Transit Tracker divides the stops into groups (see first image for an example). Instead on 50 stops in a list that is a pain to scroll though on most phones, you first pick the general location of your stop from a short list of ten or so. Next you see another short list of the stops in that area. Another way to specify a stop is by entering a Stop Number. The only problem I see with stop numbers is that you have to find out the number in the first place and then remember it. TriMet provides a number of ways to find stop numbers both on the phone and on the web. To me an ideal place for stop numbers would be on signs at the stops but the TriMet web site doesn't give any indication of this. TriMet is one of the systems that tells you when you bus will come but doesn't show the current time.