Researcher Benedict Evans Evans explored the numbers on the Facebook application pages of each platform to reveal interesting insights into usage of Facebook mobile applications. Facebook has a page for each application which mentions active users of the application.

Facebook has publicly revealed a 750 million user base. Adding up users of all mobile applications add up to 222 million, close to Facebook’s claim of 250 million mobile users.

The rest 28 million would therefore be the users who access Facebook via the mobile web exclusively. The simple addition raises a caveat. The individual app usage numbers would have duplication of Facebook users. A Facebook user may use more than one Facebook app on his mobile. The duplicate numbers, if they were known, would be the addition to mobile web users.

While the iPhone/iPod Touch (85m) and Nokia Ovi (a dismal 5.6m) figures are straight cut, the Android numbers are tricky. Several OEMs bake their own Facebook and Twitter functionality into phones – Motoblur in Motorola and HTC Sense. Facebook for Android has around 54 million users and, therefore, the OEMs would constitute about 22 million. BlackBerry’s 39.5 million figure also gives incomplete picture since several enterprises and government agencies block access to Facebook application for risk of phishing or malware.

Incidentally, Facebook for Every Phone, the feature-phone app by Facebook is doing quite good with 7.5 million active users.

The third-party apps, the OEM apps, and duplicate usage indicate that these are no absolute figures but they give a fair bit of idea about Facebook’s mobile usage.