Horace Dediu over at Asymco has put together some numbers on gaming users for the various consoles. According to his data, iOS is a contender not only for the top gaming platform currently, but for the top gaming platform of all time. Game Center currently claims about 130 million users, and Asymco says that if that number can represent all of iOS' gamers, then it easily beats out the Nintendo DS' 150 million unit sales. The PlayStation 2 is one of the biggest traditional consoles of all time, and even that console sold also about 150 million units.
Of course, the question is whether Game Center users indeed works as a representation of iOS gamers. In all likelihood, however, it's actually low. Apple has sold about 400 million iOS devices, and not all of those users have obviously signed up for Game Center, though you could argue that a large number of those users still play games.
OpenFeint was a third-party social gaming platform, and it once boasted 180 million users, which would be higher than any other gaming console ever released. iOS isn't just a gaming console, either -- lots of users may buy the devices for non-gaming purposes, and then play games on them just on a whim, as opposed to a dedicated gaming device like Xbox 360 or the PS Vita.
Whatever the exact numbers, there's no question at all that Apple is now sitting on one of the most popular gaming platforms of all time. Whether it set out to take over gaming or not is inconsequential -- the iPhone and the App Store have certainly changed gaming already, and are enormously popular, even just a few years into their lifetime.