Thanks for your help, Justin!
I tried that, but the iphone still wasn't happy.
That whole thing about applying a clear float to the br is from a Dreamweaver sample layout, and I'm not really sure how to use it. The comment says that it's to be applied div or br elements...
However, what I did that worked was to put clear: both in the #footer div. It worked, but I always worry that solutions I use will start the dominos falling!