Nice application, and nice job. Two suggestions: if it would be possible in an update to include an even easier version for little ones who can use this app as a math learning tool; and, along those same lines, if there could be a way to provide partial solutions (say, for a one or several boxes) rather than just full puzzle solutions. Also, not sure if there is a correlation, but you may want to look into this: other operations on my N900 slowed down after I installed/ran this application. When I uninstalled, speed seemed to be normal again. Thanks!

Nice implementation, I like the interface.
Couple of possible enhancement: Game Timer for completion tracking and Hint Button for single cell hints.