Using cell phones in the classroom has become my latest research topic. I am excited and encouraged by how many activities I have found that use the "pocket PCs" my students already own. The best resource I have uncovered so far is the work of Liz Kolb. Her blog, cellphonesinlearing.blogspot.com, is a treasure trove of information and resources.
I have also bought her books and have been reading them via my Kindle App on my iPad. Great activities, great research, great case studies, wonderful ideas.