without over thinking this, since I don't have a waterproof case, here's what I do. On days that it might rain, I put a zip lock bag in my jersey pocket. If it were to rain, I'd take the phone, put it in the bag and then in my pocket. Simple and cheap. If I need to look at the phone or use it, I can do that right through the bag.
That said, for my iPhone 4 I had an otter box and I just put the quad lock universal adaptor on the back of it. Better yet, what I'd do now if I were worried about water is
this.
J.