Issues in App Store when downloading apps under iPhone OS 3.1.3

Reports in Apple's Support Community suggest some users running on older iOS 3.1.3 firmware are no longer able to download apps from the App Store after Apple pushed out an update on December 16th.

Specifically, when users jump into the App Store and try to download any app, the download button is completely missing altogether. Although fragmentation within Apple's iOS ecosystem is extremely limited -- at least compared to the closest competition with Google -- some users are still running older iOS versions.

There's currently no fix outside of upgrading to a newer version of iOS, but for some users with older devices that simply don't support current iOS versions, this could become a serious problem if Apple doesn't come up with some sort of fix on the backend.

Source: Apple Support Communities via Engadget