Response to Barry
Barry,
I'm using an iPhone right now and can tell you that, in my experience anyway, you can type with one hand or two (holding the phone horizontally allows for two thumbs and holding it vertically allows for one hand/thumb).
If you want to end a call after looking at other applications or documents while on a call you tap the top of the screen which takes you back to the phone from wherever you are. You can also just push the physical button on the top of the phone to end the call and put the phone on standby.
It's really simple to use.