I'm not sure what stops EasyTaxi from working in the U.S. I use it in South/Central America and it routes regular taxis, you pay in cash like usual but get the convenience of the Uber experience of knowing a cab is on the way, and who the driver is.
At a guess, it's because it's a Rocket Internet company and the group generally does not like operating in the US for a variety of reasons (chief amongst which is that their business model is to execute ideas in emerging markets, not developed countries).