Wolfenstein 3D has been ported over to the Pocket PC by pocketinsanity. Although not the first port ever, this version will allow you to play not only the shareware versions but the full versions as well of both Wolfenstein 3D and Spear of Destiny.
The latest version has added some key features such as sound and music, lefthanded support and the ability to save and load games.
Best of all, Wolfenstein 3D is free. Note that it only comes with the shareware version game files. To play the full versions, you will need to own the original games and copy the game files over.