Hi Russell,
There was never an App but a mobile HTML version of Mygeotab/Checkmate.
I just tested the mobile version on my Android phone and it works great.
To access the mobile version of MyGeotab you simply have to browse to the MyGeotab server where your database is located in.
If you are not sure then I would advice you to access it via your computer first and look at the URL in the address bar which will look like:
http://myX.geotab.com where X is a number. All you have to do on the Android is add a /m to the end of it:
http://myx.geotab.com/m