Facebook's recently begun displaying user stats for its mobile apps for several platforms, and the numbers are downright overwhelming. The iPhone takes the largest slice of the cake with (at the time of writing) over 104 million active monthly iOS device users, with BlackBerry users at nearly 60 million, and just over 12 million using the Android client. So what can we take away from these numbers? Well, at last count, Facebook has over 500 million users, so a pretty sizable chunk of them are using mobile apps. Interestingly, the last reported number of iOS users was 100 million; that's the number announced at WWDC, just back in July -- but Facebook lists more than that amount of active monthly users, so we're not sure how these numbers are being calculated. We've reached out to our contacts at Facebook and will update if we get a clearer picture of where the stats are coming from.