1. A method of providing cost information associated with contact numbers, the method comprising: determining real-time location-specific calling cost information for a given calling plan; obtaining a mobile address book containing two or more contact numbers associated with a mobile device that subscribes to the given calling plan; mapping the real-time location-specific calling cost information to the two or more contact numbers based on location information associated with the two or more contact numbers; and transmitting the mapped cost information to the mobile device.