If I got a Vita my pockets would hate me. I would have a dumbphone for texting and calling, an iPod Touch for my multimedia and WiFI browsing, a 3DS for gaming, and a Vita for other gaming and 3G browsing.

that is exactly what I have in my bag right now. Apart from the 3G bit. Oh and mine's a Black Berry, a neither world betwixt the dumb and the smart. Mind you, I did have an Android and still carried a DS & PSP around with me.
My advice to you: you don't need an iphone. You need a bag.
On a serious note, every seasoned traveler knows that having one device that does everything is just not reality right now. I justify each of my 4 hand helds for different purposes. There is a lot of cross over in what they can do (like wi fi browsing, multi media, cameras & gaming) but they all excel for some uses and are complete rubbish for others. And I still take a book whenever I go abroad because they don't use batteries and flight staff aren't afraid of them.
In my defense - I only carry the Vita when I'm hooked on a game. But the 3DS comes everywhere for Street Pass and Coins of course.
Get a bag.