Yes you may, the Passenger App is available for free download in both the IOS store as well as in the Play Store. You can find it by typing in TaxiCaller and simply download it on your device or check the following links:
Android: https://play.google.com/store/apps/details?id=com.taxicaller.app&hl=en iOS: https://itunes.apple.com/us/app/taxicaller-for-passengers/id604708748?mt=8