Well typing on it and calling is pretty straight forward in fact typing is pretty easy considering the size (but definitely difficult with one hand). Doing plenty of other things like dialing with one hand and so on is difficult. It is especially hard since stretching a little far can sometimes make your palm touch some other parts of the screen inadvertently. Fortunately iPhones don't have the retarded soft touch buttons on the front that samsung insists on using.
So as an in between for a phone and tablet sure but for everyday use where you actually do often need to do some one handed actions it can be a pain. If you always have two hands free cool, I have small kids so I battle to have one hand free.
I should add I have a samsung galaxy note 2 and it is such an awful awful phone I cannot believe samsung does so well making such absolutely rubbish products (I will leave it at that my list of grievances is too long for a simple post). Suffice it to say my decision 2 years ago to try something other than an iPhone for a change was a huge mistake, nice for the first 3-4 months when it was new and exciting. I can admit when I was wrong.