Over 100 million people access Facebook from their mobile phones

"There are more than 100 million active users currently accessing Facebook through their mobile devices.
People that use Facebook on their mobile devices are twice more active on Facebook than non-mobile users.
There are more than 200 mobile operators in 60 countries working to deploy and promote Facebook mobile products"
Source: Official Facebook Statistics, retrieved 12th February 2010
For some reason these stats weren't updated at the same time as the total user figures, which were updated on 9th February