Most people do not even really need a cell phone, much less a smart phone. If I had a choice I would take my Motorolla brick back. It made phone calls, withstood dropping off a roof and could be used as a hammer or a wheel chock if required.
I would argue that the thing that most people don't need is a landline. I think cell phones replace them very effectively. The whole point of having a phone at home is so people can get in touch with you, so what's more efficient a phone left at home while you're out or one that actually goes with you so that you can be reached? It's kind of like insurance, you may not use it often but when you need it, you
really need it.
I can definitely see where people in certain professions might have need of a more 'sturdy' apparatus but as far as smartphones go, personally I'm a big fan of them. Phone, camera, calendar, data organizer, MP3 player, email, internet access, etc. Sure probably too many people use them more for playing games than anything else but you can't judge the usefulness of the technology solely by that. Computers are also extremely useful pieces of technology and a lot of people use them for very 'unnecessary' things too.