TaxiCaller's app lets you hail a cab directly off the map. Or you can book a ride for later. Once a ride is booked, you can track your cab's location on the map and get constant updates on the cab's location, distance and time of arrival while you wait for it!
You don't pay anything extra when using the app, on the contrary some cab companies give you discounts when booking through the TaxiCaller app.

Taxi booking is quick and easy with TaxiCaller.
The app sets the pickup address automatically by retrieving your current location.
You can hail a cab directly off the map or select a taxi company from a list containing information on how long it will take for each company to have a cab at your pickup address.
You can also enter a destination address to get immediate price estimates from different taxi companies and select the one you prefer (price estimates are displayed if the taxi company has enabled this feature).