Most taxi drivers in Beijing now use an app. I guess it works a bit like Uber to the extent that the driver gets messages from people looking for taxis in the area where he is. People leave a voice message saying where they are going and while driving the driver is notified that someone is looking for a taxi 100 meters from here then they hear the message. Not sure how efficient it is compared to just flagging one down. It's not like the Beijing taxis are lacking clients.