Thinking of buying a new 4S unlocked to be my only phone at home in Canada and when travelling. I prefer the length (shorter) and thickness (more substantial) of the 4S compared to the 5. I don't require all the latest bells and whistles. Only concern is that I need it to last 2 to 3 years from now. Will future versions of iOS negatively impact the ability of the 4S to function? Your comments would be appreciated.