I had a similar dilemma with my 4 and 5 year olds with my iPhone. They were constantly asking to use it, especially after I loaded a bunch of free or inexpensive kid friendly apps--was a great tool for learning to read, math, puzzles, and problem solving. It actually turned out to be a great tool for wrapping up potty training for my son--a reward that finally was worthwhile in his eyes
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. An unfortunate episode of the drops which led to a slightly damp iPhone (phone survived but there goes the warrantly
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) convinced me to pick up a pair of refurb last gen iPod Touch that Santa brought for Christmas. And while I hesitated, thinking this was spoiling them a bit too much, turns out to have been a great purchase. They generally lose interest in most of their other 'toys' after a while but they both have been using the iPods nonstop for the last 4 months. My nephew got a DS at the same time and now only occasionally shows interest in it. As a bonus, I no longer have to cart along the portable DVD player and endure the guaranteed arguments over what they each want to watch. Last plane flight was the most peaceful we've had yet.
Unfortunately, they both are now fascinated with my iPad ("Daddy's Big iPod"). I think I'm going to wait a while to make sure they are responsible enough caring for their iPods before deciding to spring for an iPad for them.
My advice would be to start him out with a Touch and see how it goes. But I also agree with other's advice. Use it as an opportunity to teach the value of such things--give him the opportunity to earn it. My kids didn't ask for their iPods (thankfully) and as they both love using them, I limit the time they get to use it, letting them earn time with them (doing small household tasks, good behavior, doing "homework", etc). Just my $0.02.