I've just tried the free ones and they have been single player, but you could challenge each other for times and high scrores of various word games.
Or there's always scrabble if you like that. Not really a puzzle game but it looks like it's got wifi and even a facebook connect so you can play friends with no iphone too if you want. I haven't tried this, so I can't say if it's any good or not, but it's by Electronic Arts, which is a pretty big name.
