A majority of Facebook users world wide log in only via a mobile connection. I don't think I have ever used my phone to connect to Facebook, and I know I don't have the Facebook app installed - in the minority again.
The mobile-only numbers appears to be increasing because a lot of the new users are from parts of the world where they often may not have broadband access at home, and so use their phone primarily for Internet access.
Digital Trends54 percent of all active users logged on to Facebook only through the company’s mobile site or app in the past 30 days, a 3 percent increase over the previous quarter. These mobile users use the site just as frequently as those who use the desktop site; in both cases, about two-thirds log on at least daily.