Umm...you obviously miss the point of the iPhone. The iPhone is a phone on which you can install thousands of third-party apps, some of which are quite neat. Most of these did not take several months and a few thousand quid creating.

On the other hand a Nintendo DSi is a portable games console - i.e. a miniature version of a Wii/PS3/Xbox. Nintendo DSi games generally do not help you find a taxi, allow you to use Facebook on-the-go, etc. What's more, the developers of these games take several months, and cost a few thousand quid to create.

DSi != iPhone. Some people own both, and use whatever they feel is best for the task at hand.

Actually the DS homebrew scene was alive and well last I looked, I would be surprised if there aren't aps (or, for that matter, the Ninty Opera cart) that could help you find a cab or use Facebook on-the-go (though why you'd want to use it at all remains a mystery). A DS/DSi with an R4 (or equiv) opens up a lot more options then you seem to think.

That aside, a PSP can do most of what iPhone does -- including make phone calls (Skype) -- right out of the box. You need a Wifi connect to do much of that, of course, which limits the utility of the phone part, but I dare say the games are WAY better then the iPhone. Beyond that, if you have anything but a 3000 (and with the recent release of the tiff exploit and ChickHEN even that's mattering less these days) there's a world of homebrew to explore. As is the norm with such things, some of it is amazingly good (better browsers, for starters) and some of it... Less so.