Thanks to the Hide & Seek festival in London this Sunday, I played two interesting games using a mobile device.
Playing And I saw was about simply messaging a 6 digit shortcode to a designated telephone number. So it could be played by old and new phones and didn't require the mobile Web. However if you did have a "mobile Web enabled phone", you could look up the status of the game which is as useful as a twitterstream, i.e. very useful. I enjoyed bumping into people around Southbank and exchanging shortcodes with other short-coded players and finding coded nearby objects.
The Go Game makes explicit use of the mobile Web to
give challenges to teams and co-ordinate the whole game. It was interesting to
hear the game's organisers give the introductory talks and make special note of
problems concerning Blackberry's browsers. 
Unlike the previous game, you
play in a team and you also can do inter-team challenges. It's a lot of fun and
you should try it!
I've been waiting a long time for a good game on the mobile. And this weekend I feel like I've finally hit that milestone. Not only have I now played a worthwhile and enjoyable game using my mobile, I have confirmed that theory about mobiles being more social and immersive is so very true.