That's all changed recently because I've jumped on the bandwagon and purchased an ipad. It surprises me to say this, but it's a handy little device that I'm finding myself using constantly. And of course, it's great for gaming. Whether you're competing for mayorships on foursquare or downloading an addictive casual game to play during your spare time, the ipad is great for gaming. Of course, I'm sure an iphone is is great too, but I haven't sold out that much just yet...
Although not quite a "game", Foursquare is my favorite so far. I'm sure it's much more convenient to play on an iphone, but I'm still very addicted. Robot Unicorn Attack is a surprisingly fun, high quality game that I downloaded right away - you can also check it out free online here: http://bit.ly/d4am53. I keep meaning to try out Pocket Legends as well - a full MMORPG for iphone and ipad. And it seems like tons of new games are coming out all the time. I'm also having tons of fun with Angry Birds.
Definitely plan on exploring some more games on my ipad. Any suggestions out there? I wish they'd port Pocket Kingdom!
Edit: ZOMG!!! I just discovered Battle Bears and I love it! Violent, hilarious and addictive. Check it out if you have an iphone or ipad. http://www.battlebears.com/