Ditto iPad 3 ("New iPad") upgraded from reasonably-functional iOS 8.1.3 to iOS 8.2 ("reasonably" because iPad's been much slower and less-stable since upgrading to 8.x from iOS 7.x, but it generally works).
iTunes & App Store appeared functional, presented apps that needed updates and allowed me to search for new songs to purchase.
Attempt to purchase new song simply flashed from "Buy Song" back to the price ($0.99) as though nothing had happened.
Attempt to update apps listed in "Updates" likewise simply flashed back to list of apps requiring updates when I tapped "Update All."
Went to Settings->iTunes & App Store and attempted to "View Apple ID" -- dialog simply disappeared.
Tapped "Sign Out".
Tapped "Sign In" and got "Cannot connect to iTunes Store."
Experiencing same (Attempt to purchase new song simply flashed from "Buy Song" back to the price ($0.99) as though nothing had happened.) on iPhone 6 Plus running iOS 8.2.
Attempts to search iTunes Store for song from iPad Mini Retina running iOS 7.1.2 initially replied with "Cannot connect to iTunes store," then produced song and appeared to allow purchase, then responded with "Error."
...so issue would appear to involve AppleID/iTunes Store connectivity, rather than iOS version.