zTrip sounds identical to an app I envisioned in 2010 I called "Yo Taxi!" It would take your phone-reported GPS location and send it out to one of the affiliated taxi services (depending on who serves that location, cost, etc.) who would dispatch a cab to that point.

I'm kind of glad "Yo Taxi!" exists in some form now, what with the wheels (figuratively) falling off Uber and Lyft.