iPhonus Sudoku free is a sample game of the commercial application. You can try iPhonus Sudoku (demo), which is free demo version with limited functions. To play the game you must

Main features:
- over 40000 puzzles in 5 difficulty levels
- hints, pencilmarks and optional checking for incorrect moves
- skinnable

iPhonus Sudoku costs $9.99. Check out the web site for more information. Try with TestiPhone