Mark Zuckerberg stated that 25m users are accessing Facebook via Facebook Mobile each month. The mobile user base has jumped to 15m.
The are 1.64m iPhone users accessing the site, closely followed by 1.56m Blackberry users. Another 1m come in from other sources (these are only accesses from officially sanction Facebook Mobile clients or through the mobile portal).
Opera reports that Facebook was the most accessed site through it’s Opera mini browser.