The N-Gage was an interesting hybrid: it was a cell phone, but its games came in cartridges like a regular handheld. This was tremendously inconvenient, you had to open the back lid and remove its battery to change games. The controls were clunky, and the screen was tiny. A second model was quickly introduced and fixed many of its issues, but it was not enough to fix its reputation. The name was later reused as a game download store for the Symbian S60 series, but that's also long gone.
While it is often mentioned in lists of "worst consoles ever", that's somewhat unfair: the N-Gage was quite ahead of its time (remember, this was long before smartphones became mainstream), and its fans swear that some of its games were actually pretty good.