The iPhone won't be challenging the Nintendo DS any time soon
So... airports... hanging about... I decided to buy a game for my iPod Touch and chose Bejewelled 2. It's nice looking, fun to play, it reminds my why I should never go near that game on my computer because it's a huge time sink.
I guess I played for about 40 minutes before my fully-charged touch batteries were down to <20% and I got the battery warning.
I don't own a DS but I hear you can get in the region of 10+ hours of play time, maybe as many 14 with the brightness down. My Touch could maybe do an hour. Battery life seems fine for other things: browsing, watching movies, playing music. But whatever Bejewelled was doing (using the 3D processor maybe?) ate the battery with fava beans and a nice Chianti.
Maybe the iPhone has a better battery than the Touch but I can't imagine it's much more than 2x better. My Touch is also getting on for 9 months old so it's battery is probably 15% from it's new capacity. Even so you're looking at a device that may go 3 hours tops.
I don't think Nintendo have much to worry about at this point.