A change that was made to the App Store, possibly on the 16th of December, was causing problems for iPhone and iPod touch owners running iOS 3.1.1 on their devices. The problems were not being able to download apps - clicking on their price, other buttons such as ratings were also broken, and some app screenshots weren’t available.
Over on the Apple Support Communities, an initial post by one affected iPhone 3GS owner has already grown to several pages, as users reported their own experiences. While Apple can’t keep supporting older devices forever, these problems seem more like a glitch rather than an active move to end support.
Eventhough now it seems Apple has fixed this problem and everything runs smoothly!