There are probably more games coming out for PSP than Ngage.
Anyhow, if you really want to play portable gamings, you might be better off getting a normal cell phone and a dedicated gaming system, like a DS or a PSP. Or maybe even the Gameboy Advance Micro(cell phone sized gameboy), many ngage games are technically worse than GBA games.
Besides that, I believe Gizmondo has a cell phone attachment(and has even less games), there are cell phone pdas(smartphones, and perhaps attachments for normal pdas?) that would blow ngage away, and then there's the upcoming ngage2, which is supposed to blow even the psp away in specs.