IBM has released a toolkit that provides developer tools and a Java runtime for building web service apps accessible by Windows CE-based Pocket PC, Palm OS, and BlackBerry devices.
Here's an excerpt from this InfoWorld article written by Paul Krill:
"What we're providing for each of these platforms is a Java implementation using source code available in an open source way to let you receive and send Web services messages," said IBM's Bob Sutor, director of Web services strategies in Somers, N.Y. Eventually, IBM plans to add other platforms, including cell phones and pagers, as supportive platforms for the development kit, Sutor said.