The OP's prediction has to be based on the 1billion ios devices PR announcement a while ago, but even at that joke figure, Given that I have 2 of those devices and I would not invest money in itunes ever then you have to factor in that a lot of the 1billion devices are either cases where many devices are owned by a single person and have 1 account on them (even 2 devices per person would half the number to 500m potential sales with 100% of owners buying it) and then you have to factor in of the 500m potential users of iDevices how many of those actually ever use their phone for anything other than just being a phone, let alone how many would ever consider spending money or time on a game, you are looking at maybe 1 in 10 so cuts down the potential buyers of the game to close to 50m at best, given Mario's attach rates on consoles are pretty high I would wager this will life time sell around 5-7m copies of the $10 version based on around 10% of the gamers on ios
This is just based on the ios version of the game and not taking Android into account, it is far harder to nail down numbers for android devices which are actively in use.
Regardless of anything though, to think you're going to get 300m sales on 1billion devices is insane.
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