On top of Facebook’s new stats last week — the company said that 400 million people are using it every month — there’s another update today. One in four of those users, or 100 million people, are accessing Facebook from a mobile service every month.

In September, Facebook said it 65 million monthly active mobile users out of 300 million monthly actives, which at the time was a 300% increase in mobile users from a year prior.

Which services? Chamath Palihapitiya, Facebook’s VP of Growth, Mobile and International, shared some more details about recent updates. Here are those, including our take:

Mobile sites: Both m.facebook.com and touch.facebook.com (the long-existing web version of Facebook for iPhone) have gotten upgrades recently. While the mobile site has 18.2 million monthly active users (MAU) and 6 million daily active users (DAU) according to AppData, we should point out that Facebook also notifies users of the mobile site if there’s a Facebook app available for the handset device they’re using, in conjunction with GetJar. This means that new users to the mobile site are getting redistributed elsewhere.

Texting: In an update to previous stats here, Facebook has worked with more than 80 carriers in 32 countries to let people use texting (SMS) within Facebook, meaning they can do things like update their own status, get texts about their friends updates, etc. Palihapitiya also confirms the launch of Facebook’s URL-shortening service, fb.me, saying the company intends to use it for texts and other mobile notifications (rather than as a direct competitor to Twitter-oriented services like Bit.ly).

Applications: New updates have come to apps for mobile operating systems/devices including Google’s Android, Blackberry, iPhone, Nokia and Samsung; other apps are availalable for HTC, INQ, LG Electronics, Palm, Sony Ericsson and Microsoft’s Windows Mobile. Out of all of these, the iPhone app continues to lead, with 26.2 million MAU and 13.7 million DAU as of today — it is one of the biggest and most heavily used apps out of any on the platform, and that’s counting social games. Blackberry’s app comes in second with 13.8 MAU and 8.35 DAU.