I am looking for the API which will provide me bus routes. In general I need the API which will give me all the bus stop locations latitude/longitude by entering the source and destination. I want the bus stop points between source and destinations. Can anyone help me with that API? Waiting for the API reference! I need to use this API in iPhone.
As I said in my comment, there is no universal "the api" for bus routes. However, Google has set up something called the Google Transit Feed Specification which is just a spec whereby local transit authorities can make their information available to Google Maps.
Here is a list of all the US transit authorities that make their information public in this way:
http://code.google.com/p/googletransitdatafeed/wiki/PublicFeeds