the N-Gage and the N-Gage QD (Quesedilla Edition) is probably the worst excecution of a decent idea. Basically what they did was what microsoft did: They said "Wait a minute! we can give the gaming market a shot!" and rushed it out the door because kids are ignorant and stupid and will buy anything that beeps and bloops.
Unfortunately for them, they were dea wrong. That, and its pretty easy to see that when you throw in an MP3 player, a phone, and a gaming system into a small little peice of plastic, its gona cost. And people don't generally buy things that aren't worth the money. Generally....
The PSP, while it is nice, has its flaws too. But the PSP is part of the new generation of gaming, while the N-gage is like.. long long behind this generation. I wouldn't even consider it for debate.