Every copy protection is crackable, so it was only a matter of time before Nokia his N-Gage protection would be cracked. Some people have already found out how to play N-Gage games on the Siemens SX1 mobile phone. It is expected that Nokia N-Gage games will work on all mobile phones based on the Symbian OS like the Sendo X, Nokia 3650, Nokia 3660 and the Sony Ericsson P900.
Images of SonicN running on the SX1 can be found here and according to users in the forum other games work as well even on other mobile phones. But playing games on the N-Gage his keyboard will still be comfortabler than on other phones I think.