I have another option for you, unless you are totally set on an iPhone.
I've got the Casio Commando and it doesn't need a case to be waterproof. I've shot photos and sent them places while the phone was under water. All the access ports (battery, audio jack, USB) are O-ring sealed. Any external connections are gold-plated to avoid corrosion. This is the same phone that is issued to DPS officers around CG (and maybe other places) because it is so rugged out of the box. It runs Android. It is on Verizon. I love mine.
Again, if you are set on an iPhone, that doesn't help, but if you are looking for options for to make a phone life proof...
"The only thing we did was wrong was staying in the wilderness to long...the only thing we did was right was the day we started to fight..."
My book, The Marauders on Lulu