IMHO:
N-GAGE sucks!
Okay, it really sucks!
Bad game cartridge design -- this is the main reason I will not get one. I don't want to take the battery out and so forth just to change which game I am playing. It's cumbersome.
For on the go game playing...
Tapwave (
www.tapwave.com), PocketPCs, GP32 (
www.gp32news.com) , GameBoy SP and the future PSP are more to my liking.
I have a PocketPC (run Tao-Group's Intent on it) and GameBoy SP, looking at getting a Tapwave or GP32 soon.