well, you copy the CAB to your smartphone using active sync's Browse function. go to smartphone, my device, storage, windows, start menu
there you copy the app. or somewhere else, if you have a filebrowser on your smartphone i.e. resco explorer.
then you open the CAB file on your smartphone, with your smartphone. either using the filebrowser or reboot your smartphone, and open the file in the startmenu. it'll install the app, remove the CAB file and place the shortcut into the Accessoirs folder of your start menu.