I think this is a great idea, but from a practical standpoint, it's kind of difficult. Speakers and mics require openings and I know that there are things that can be done, but they aren't easy. Essentially, to make this happen, you'd have to design a sort-of cover for the whole phone.

But on two occasions, I've lost phones simply by getting them wet. One still in my pocket.

A waterproof cellphone would cost more to make. I can see offering waterproof models for people who are willing to pay a little more for them, but there will always be plenty of people who are willing to risk it to save some money. Both should be available.

It might be possible to use a cellphone that has been placed in a thin plastic bag with a sealing strip to make it waterproof. I don't know of the sound would be too severely minimized through the membrane of the bag to make it unusable but it might be worth a try.

They have a phone like this already, I think its called the boulder. Here's a link to some info on it. http://www.mobiledia.com/phones/verizonwireless/g-zone-boulder.html