I have a waterproof case for my iPhone which I've used in the swimming pool to take videos of my kids.... Very good.
http://www.amazon.co.uk/IPHONE-WATERPROOF-CASE-COVER-SHIELD/dp/B005CNGTIWFor sat nav, which I now rely on to get me places (!) I use the native turn by turn navigation through the Bluetooth connection on my radio. Audio only - but it works well.