This popular game that doesn't really need an introduction, Sudoku -
now in a version made by me. Play the game on your cell-phone, and if
you need more levels you can make/enter them into the game via the level
editor. In theory suitable for all MIDP2-compatible mobile phones, but
only tested with Sony-Ericsson k700i.
If you're unfamiliar with the game, it is a game of logic where the object
of the game is to fill a 9x9 grid with all the numbers from 1-9 without
reusing the same number within a column, row or 3x3 squares.
The later versions of this game also supports downloading new levels from
a server using GPRS or WAP. The number of levels available will hopefully
increase over time, but this is dependent on people adding sudoku-levels
via the "Add level"-page.