What exactly that meant wasn't immediately verifiable, but once the update was installed, it became clear. AT&T got what it has wanted since last year: a 4G symbol in the iPhone 4S status bar.
AT&T's network supports HSPA+, which as we've noted before, isn't really 4G, but more like 4.5G. However, since there's no LTE iPhone, the 4G in the status bar gives the AT&T iPhone 4S a distinct --- and visible --- advantage over the Sprint and Verizon versions (it has a real-life advantage already in that actual speeds are faster on its HSPA+ network than on the others' 3G CDMA networks).
Other new features in iOS 5.1 include a camera shortcut on the lock screen, which had been previously rumored, as well as the ability to delete photos from the iCloud Photo Stream. There are also bug fixes, including one for a nasty bug which caused audio to drop for outgoing calls, and of course some battery life fixes.
Apple also released iTunes 10.6 on Wednesday, which includes support for 1080p video downloads from the iTunes store.