I had an N-Gage and I was quite fond of it. Do to it's age, the internet, text messaging, and overall presentation of the phone is just a little outdated. The idea of being able to swap "game cards" was quite an innovation at the time and most of the games were something that most other phones at the time couldn't hope to offer. The original N-Gage offered MP3 playing and had a built in FM tuner. The major downside of the phone was the concept of "side talking". The microphone and earpiece were both on the top of the phone so when making or receiving calls, it looked like you were talking into a taco. You also had to turn off the phone and remove the battery to access and change game cards.
The N-Gage QD was Nokia's supposed "upgrade" to the phone. It was smaller, offered an easier to decipher keyboard (when playing games), had a more comfortable and usable D-pad, and had a longer battery life. It also included a button that could be pressed that would automatically start a game when a game card was inserted without having to navigate the menus to get to the games icon. Game card access was moved to the outside of the phone so you could "hot swap" the game card without shutting off the phone. The MP3 player and FM tuner were removed from the design to lower the price of the phone. The full color menus were also replaced with black and orange themed menus. The rubber ring that encircled the outer edge of the phone was also notorious for stretching and deforming over time from the heat and moisture of your hands when holding it as well as opening the dust flap covering the charger and game card slot.
The phone had a decent roster of 53 games that ranged from FPS, Racing, Strategy, Action, and RPG. Some of the more popular games was Elder Scrolls, Rifts, Warhammer 30,000, and Ashen. The phone was also capable of playing java phone games and apps rasing the total number of games/apps for the phone to over 1000+ (estimated).
The phone is still nice nowadays, but it isn't good for anything but playing N-Gage games and making phone calls now. Don't think internet is even possible on them now either.
Didn't want to push possible interest away from your topic, but figured I'd give a short description of the phones so people know what your offering.