I had been carrying my iPhone in my jersey pocket but didn't like that very much. My LBS stocked a BiKase so that it was I tried. It is a neoprene case that zippers closed. It has a window to see the phone and the touch screen works thru the window just fine.

I attach it to the thicker tubes of my Cannondale just fine, but it is a bit loose on my C&V bikes.

http://bikase.com/