The choice of AIM compatability irks me (Boycott AOL). If it ran PocketPC or Mobile Phone Edition I'd be all over it
I've had a little use with the T-Mobile Sidekick (AKA Danger HipTop), and I think the engineering and design are incredible! I'm so glad the Sony PSP didn't rip this off because I can suggest an alliance with Danger to Nintendo for their Next-Gen portable

No, I don't think n-gage is a good idea. If it could play decent games, screw the phone capabilities!
If you've ever held the thing... it just *screams* "GameBoy". The area behind the screen feels more comfortable for your index fingers than the L & R buttons on any console. The area revealed below by the flip-up screen seems adequate for a six-button arcade layout if only widend a little. The GBA SP's sub-surface D-Pad and buttons could easily fit. Minimal controls when closed could be positioned on either side for two-player single-GB games (Jog dials and such similar to what remain on the current Sidekick).
Ah, one can dream.