C2Doom for Series 60 smartphones by Markus Mertama is probably the best mobile doom available. Full audio, up to four players multiplayer modes over bluetooth, Doom shareware, Doom1, Doom2, TNT and Plutonia WADs supported and many other features as savegame exchanging and reconfigurable keyboard mappings. The N90's 352x416 pixels screen is also supported!
http://koti.mbnet.fi/mertama/
