Houdah Software (http://www.houdah.com/iPhone) has released ACTSudoku
Easy for iPhone and iPod touch. ACTSudoku Easy offers all the
features of ACTSudoku Unlimited for free. Those features include a
streamlined interface, advanced game generator, automatic markers,
intelligent hints, and more.

ACTSudoku Unlimited (US1.99) improves upon ACTSudoku Easy by offering
three levels of difficulty. All game boards are symmetrical and
guaranteed to be solvable by logic only. No guessing or backtracking
is required. The most noticeable advantage of ACTSudoku is its
intuitive touch interface, which sports both positive (green) and
negative (red) markers (pencil notes), according to the folks at
Houdah Software.

Both ACTSudoku Easy and ACTSudoku Unlimited are available at the
Apple App Store.