I used dish towels to hold the phone for two reasons, the first was that I was not sure if the plastic jar was water tight, I figured the cloth would catch any water before it got to my Blackberry and the second was that they worked well to hold the phone in the jar without scratching the face of my phone.
Please only use plastic for this as you should never introduce glass to a swimming pool.
The materials and complete process for the build are all in the video as I took the concept of showing someone how to do something in 30 seconds on video to be very literal. I even added a demonstration of the camera in action. I hope you enjoy this Instructable at least as much as my daughter enjoys blowing bubbles underwater!