I bought one of these, off this ebay seller, with a 1" RAM ball attached.
http://www.ebay.com.au/itm/Dedicated-Waterproof-Tough-Case-for-the-Samsung-Galaxy-S2-SII-i9100-/140856169805?pt=AU_MobilePhoneAccessories&hash=item20cbae954dI have ridden through some pretty heavy rain, for many hours at a stretch, and never had a problem. USB tails out of the bottom and is powered by my "cig" lighter outlet. Screen is touch sensitive (it must be a conductive). Works just as if there wasn't a case. All buttons are still accessible from the outside of the case. If I have a problem, it is that I have to remove the phone from its usual gel cover before it goes into the case. I leave it in the case until such time that I no longer need it to be waterproof. In reality it only takes a few seconds to remove the phone from the case, or the case from the phone - whichever way you want top look at it.
I always use the supplied lanyard as a safety, but thankfully, have never needed it.
Serves as my music source, GPS and phone, all through BT. I use a Finn Moto (
www.finnmoto.com.au) cheap as chips BT set. Does almost all of the things I want it to. Also allows me to make a call (to the last dialled number), even if separated from the bike (up to about 100 metres) - one of those features you aim to avoid having to use. I would never make a call when riding, but will receive one if the situation allows it to be done safely - if not I can reject incoming calls at the press of a button on the BT. No big price-tag either. I can also chat to my pillion, when she feels the need.
Lots of other models available
Buying "Big Brand" technology can become very expensive if you want to experience anything near the bleeding/leading edge. The Finn Moto will most likely work at least until I want to "upgrade".