If he's running Linux I'd be hesitant to recommend an iPhone 4, but I've never tried. I suspect lack of iTunes would be annoying. Is there a good iTunes substitute on Linux now?
I'm not sure how it would be if I couldn't as every so often i do sync some music or movies. But cloud services are making iTunes and the USB cable more and more irrelevant.
It's a shame Apple is so bad at cloud services itself.
Software upgrades require iTunes, but I guess as long as you have access to an iTunes equipped box sometimes. As you point out, if you're dependant on adding Music and Movies frequently it would become a pain in the ass.