Before I answer, does anyone actually know sales numbers for the N-Gage. I'm not sure about Europe, but there seems to be absolutely no type of publicity for the new N-Gage service here state side. I'm just curious if there is actually any software being developed for it by larger 3rd parties or not? To be honest, if it wasn't for forums, I don't think hardly anyone over here would even know it launched already. There have been no commercials or printed ads of any kind that I've seen, even in gamer magazines.
Anywho, I guess that answers your question in a way. It's probably not going to make a dent in Nintendo, Sony, Apple, or Google's sales.
Honestly, I think it would have been much better for them to make a game service (like what they have now, to compete against Apple), but just call it something other than N-Gage. I personally know a couple of people who have phones that support these N-Gage games, but they refuse to even try it because of the horrid experience they had with the first handheld.
It's almost like Sega coming out with a new handheld/phone and calling it the Gamegear Mobile. Dumb idea.