Erik pointed out a good overview of IBM’s Wireless Toolkit.
To take this to its logical conclusion, Nokia’s Developer Forum points to kXML-RPC, a J2ME XML-RPC implementation which looks really lightweight. Of course, you could always use kSOAP if you really wanted to.
Brain: Pinky, are you pondering what I’m pondering?
Pinky: Uh, I think so, but how are we going to fit a SOAP stack AND a monkey in a cel phone?