Yes. The iPhone is unquestionably more useful to me than my Blackberry was, just because the app support and mobile browser is so good. I find myself using the data about 10x more often than I did with the Blackberry.

I haven't had a regular "free" phone since 2003, so it is hard to compare. Having constant access to email and the internets seems so essential now, I don't think I could rationally compare the value to of the iPhone to a phone that doesn't have a data plan.