A new version of Facebook’s iPhone app is now available in iTunes. It follows up on the one released a couple of weeks ago by adding support for Apple’s new iOS 4 software. The new 3.1.4 version includes features enabled by the latest version of the operating system, including fast application switching and high-resolution icons. It also has some minor bug fixes and translations into Russian and Korean — two of the few markets that Facebook has yet to do well in.

The previous release included the ability to watch videos, view and write on Events walls, and upload photos up to 720 pixels wide.

Along with many other apps, this one appears to have been undercounting monthly active user data until the middle of last month. A change on the 16th showed it with 54.1 million MAU, up from a slowly-climbing 37.1 million MAU the previous day, according to AppData. It now has 56.3 million MAU. The daily active user count did not see a similar surge, growing slowly to 20.6 million today.