I don't know how many people on these boards have an n-gage, but it is quite literally a game deck AND a phone. I know there's a common perception that it's just a phone with good game handling - but it's actually quite good enough to compete with the Gameboy Advance, and some games are DS level.
There are a lot of homebrew games for the N-Gage, as it is a symbian phone, any symbian s60 program will run on it.
And therein lies the rub - Nokia botched the handling of the advertising so badly that they let the taco design get ahead of it. How many phones have mp3, video playback, bluetooth, usb connectivity, mmc capability, video game capability, stereo playback and fm radio capability for under $200?* Of those, how many are built on the vaunted symbian platform?
I can honestly say that I used the game features as frequently as the other symbian software - profimail to check my gmail, agile messenger to instant message, opera to browse the web.
But the only thing anyone ever really noticed about the n-gage was the side taco (I used bluetooth, never was an issue). *Nokia fixed it, but they took out the fm radio, usb connectivity, stereo playback and native mp3 support (easily fixed, but for a newbie, could be confusing).
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I don't think there's any value in competing with Nintendo, however. Even if you have a killer app, it's also going to be on the gameboy because of its installed base. I love my n-gage because I don't have to carry multiple devices. Many developers aren't crazy about Symbian, either.