It's going to vary person to person. Yes, Sprint users with a Pre might spend less in 24 months then an iPhone user. And some iPhone users with AT&T are going to spend less. It all depends on their needs. Rollover minutes are going to be handy for the people making long calls around the holidays to relatives. 7pm nights are going to be handy for other people. Neither feature really makes the other side invalid.
Text plans, that is where I'll agree that AT&T is definitely ripping off their iPhone users more then Sprint is with Pre users. My needs are met by their $5 plan though, with no need to go to the full $20 a month. The initial iPhone included 200 messages a month as part of the $20 internet plan.
Overall, the differences are so minimal, that I highly question the "saves a lot of money" statement. Even with the $20 unlimited text plan factored in, you are still only talking 6.39 hours of work per year to make up the difference, based off the
tech workers average wage in 2008. Bringing it down to the
common average still only results in 12.36 hours. (both figures pre tax, so a little more should probably be factored in, but the ultimate point is that the difference is pretty minor in the grand scheme of things).
I am curious, does anyone here actually pay for the full unlimited plans offered by carriers? I personally would he happy to just drop the voice part of my plan all together, and use prepaid minutes instead.