Here's a leaked video of the upcoming Samsung Galaxy S 4. It's typical Samsung design but for some reason, I think it's better than the S3, which is a very good thing.
It's approaching the size of the Galaxy Note 2, so you'll have to decide if you putting this thing next to your head is something you want to do. I've already decided any calls I make will be via a headset for devices that are 4.5" and up.
As you can see, it's definitely comfortable to use with one hand for some functions. I personally never bought into Apple's stance on the iPhone having to be used with one hand. I get what they're trying to say but you can design a phone and apps for one-handed use especially if you do a lot of scrolling.
Samsung has recognize that phones aren't just phones anymore. They're mobile devices for a fast evolving society that wants to do more on the go. They figure bigger screens could be key. I agree. There's still a different between these phablets and tablets. The line is still quite distinct if somewhat fuzzy.
Still, consider this is the size of a moleskin notebook, I'm gonna welcome it as a productivity and media consumption device, but not as a phone.