Centacto Consulting has ported their Tetris-clone Smartris from the Smartphone to the Pocket PC. They tested it on both the HTC Magician (also known as iMate Jam, MDA Compact, XDA II mini and other monikers) and the iPAQ 5450 but it should work on Pocket PC Devices, version 2002 and up.
The game also comes in a Classic version and a Modaco version. The only difference, as far as I can tell, is the backgrounds.
Smartris is free.