Classic Sudoku, in case you didn't know, involves placing the number 1-9 numbers into a 9x9 grid (split into smaller 3x3 grids), so that every square in a row, column or small grid has a unique number. Each puzzle begins with some of the numbers already entered for you, and it's your task to correctly position the rest. To place a number in a square, you highlight and then hold the relevant key on the numeric pad of the phone. Tapping the key places a temporary mark in the square, allowing you to make a note of possible answers.
The other modes included are; Mini (which uses six numbers and smaller grids), Neighbors (adjacent numbers must add up to a certain amount), Even Odd (no two even or odd numbers can be placed next to one another), X Sudoku (the two diagonal lines of 9 must also contain unique numbers), Compare (numbers will have greater than or less than signs by them, indicating whether the adjacent letter is higher or lower), Word (standard rules, but letters replace numbers), Kakuro (a different, crossword styled puzzle game), and Picture (place coloured squares into the grids, in the sequence indicated by clues).