I think the combined competition of the existing iPhone (not to mention the iPod Touch) and the apparently upcoming Playstation Phone could be gravely serious for Nintendo. It doesn't matter if most of us aren't interested. What matters are "the masses"...the ones who don't visit this forum. My gut feeling is they're going to choose all-in-one devices. Mobile phones killed the phoneless PDA market.
It's too late to change the 3DS. But Nintendo's first revision of it should include a phone. Put the phone on the outside and 3D dual-screen gaming on the inside. And keep it smaller and less power-hungry than a toaster oven. Good luck, Nintendo.