While Uber uses their mobile app (and SMS) to connect riders with private “balck cars”, Hailo is deployed in London to regular taxicabs. When you launch the iOS or Android app, you can see free taxis near you on a map. You can hail one, and it comes to you. You can then pay for the ride within the app via stored credit card.
Interestingly, there’s no special equipment involved, or even enterprise-level deal with the taxi companies. Taxi drivers can adopt this system on their own, with just their smartphones. Another differentiating point is that your fare is the standard taxi fare, rather than the premium pricing model employed by Uber.
There are obviously pluses and minuses to each approach, and wit will be interesting to see how this space evolves.