Keeping your phone dry?

I use a ziploc bag presently but I think Ortlieb claim you can make calls and text while it's in their bag.
That's useful to me, but would like to know if that's only under certain circumstances or whatever...

What do round-the-world cyclists use?
Or yacht-owning-motherfuckers?

iphone still operable through a ziploc bag. I use them, also cheap.

or you can buy a ziploc bag for $7.50

http://mash.myshopify.com/collections/all/products/waterproof-jersey-wallet