Suavblanc: I know that they did, at one point. I assume that they still do. It's buried on their website, and you'll have to provide a statement from a doctor, but there is a data/SMS only plan. Lemme see if I can find it.
EDIT: Here you go. $40 for iPhone, $50 for iPhone 3G.
http://www.wireless.att.com/about/di...for-iphone.jsp