Yes you can but remember when you have the smartphone sat nav on it is using up part of your data allowance, not sure how much it uses sure somebody will inform you. There are sat nav apps that you can download onto a smartphone too.
I recently downloaded NAVFREE for using with my Android phone. This downloads the maps at installation so you don't have to use any of your data allowance but just have the GPS switched on. It got me to Portsmouth and then from Caen to Brittany. It can get a little bit confused sometimes but hey IT'S FREE.