I recently bought the Tracks4Africa Android App. R800 from the Google Play Store.
It is really useful for exploring route options and navigating the Tracks4Africa routes and alternatives even when you don't have a signal. The usual problem with most phone mapping apps is that you either need to cache maps of the region ahead of time, or you need internet.
The problem with my Zumo 550 is that unless you have explored and planned the trip in advance on your PC, you are pretty much at the mercy of the device if you need to plan something different.
All these problems are elegantly solved with the Tracks4Africa app:
I still use the Zumo because it is on my handlebars and gives speed and eta while I am riding, but if I need to navigate a new route en route, I will program it into my phone and follow the voice prompts via bluetooth.