Could you do it? I think most people see actually scared to, but me, I have bags under my eyes from using my iPhone every waking moment. Especially during the wee hours of the morning. My head hurts. I don't know whether to go to sleep or stay awake.
The problem isn't the iPhone. It's the person using it.
That said: I had to do without a smartphone of any kind for a week and a half, and itd wasn't planned or by choice, which I think is the real acid test for whether you can go on without one. This was a couple years back, and my 3GS got stolen the same day the iPhone 4 was announced. I lucked out and managed to pre-order a 4, but that left me with about a 10 day period where I had no cell phone at all (under the advice of an AT&T rep who felt that even putting a replacement SIM in a cheap cell phone would mess up my upgrade eligibility... no idea if that was true or not, but I didn't want to take any chances of my pre-order getting punted over it and leaving me without a smartphone for even longer).
I survived the ordeal, and I did notice that my behavior changed a bit. I noticed people around me a bit more because I couldn't glue my face to a screen. I slowed down and relaxed. I used my work-supplied landline a lot more, and had a little laugh at the fact that I had become lousy at remembering people's phone numbers because I was used to having a contact list to choose from. And I was even lousy at dialing because I had been so used to my phone having a backspace key (though, at work we've since ditched the old analog phones and switched to VoIP phones, which have both contact lists and "smart" dialpads with backspace keys).
And in fact, when my iPhone 4 did arrive, I didn't tear the box open and activate it right away. I enjoyed my last few hours of no-phone bliss before getting home from work, giving my new phone a full charge, and downloading 30GB of content to it.
But would I say I would
want to go through life without one? No. There
were some real moments where not having a smartphone, or cell phone of any kind, was a real issue. I had a trip that same weekend that didn't go as well as it could've because I couldn't reach people, and they couldn't reach me. The roadtrip was also a bit boring because I had to make do with any CDs I'd thought to burn, instead of just plugging my phone in and playing whatever I wanted to hear off that (I also learned that radio really sucks these days). And there were some tense moments that could've been avoided if I could've gotten an e-mail in a timely fashion, and sent back a quick response.
What not having an iPhone for a week taught me was moderation. Gadgets in themselves aren't bad, it's how we
choose to use them that could be a problem. Getting rid of them though, isn't a good solution either. You just have to learn self control.