As far as i know, there are three themes for smf. I dont remember the urls but i can tell the names so that you can search them.
the curve one has one benefit that its author has released an auto switching mod, so whenever a mobile user visit your site, he will be automatically shown the curve theme, while desktop users can still enjoy your main theme.
Smf itself has three versions for handheld device.
1. Wml version at example.com?wap1
2.wap 2.0 version at example.com?wap2
3. Iphone version at example.com?imode
i think we need a theme like gomobile created for mybb, if some one create like that, it will help us all very much, or if smf team brings a mobile theme which has registration feature, attachments capabilities and showing avators in posts, posts counts etc then it will be much help full. Because due to mobile browsers, people are able to use websites with huge pages so the mobile themes should have a twist.