Pricenoia mobile is a java application (j2me midp1.0) that can be installed in your phone and allows you to use the Pricenoia's price comparison anywhere.
Enter the book's ISBN and get book info, reviews, price comparison and the price evolution graph on your mobile. You can now check Amazon prices at your local bookstore when looking at a particular book.
If you can donwload and play games on your mobile, you have lots of chances to have a Java phone. Pricenoia Mobile is a generic application made to run on almost every java phone out there, but some older ones may no let you connect to the internet (needed) or may crash randomly.