Living in New York city, you certainly use the yellow cab at some point - here is a great article by Tim Herrera as New Yorkers soon will have technology to help flag down a cab: http://www.amny.com/urbanite-1.812039/as-tlc-approves-smartphone-cab-hails-here-are-the-apps-you-ll-use-1.4413575
Mainly about New York and Countries of the World. Variety of information and tips