Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Just keep it in your pocket and you'll be fine. Roller coasters keep you secured the seat very, very tightly around the waist and shoulders.
 
Lol, speaking of which, I went on a water ride yesterday at our amusement park and my phone got soooooo wet from it. Clearly, I wasn't thinking straight when I decided to go on it. But immediately afterwards, I turned it off and it still works fine. I'm surprised it didn't stop working.

But when I go again, I'm probably leaving my phone in the car.
 
For wet rides use a ziplock bag of some form or flavor. I have used them when I was jumping out of aircraft on questionable dropzones for just in case. Injured or off dropzone.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.