OTA Updates/iPhone

iPhone
Users still on iOS 5.0 or 5.0.1 must update to 6.1.3 via OTA prior to installing OTA updates for iOS 8.0 or newer.

Users still on iOS 5.1 through 7.0.6 must update to 8.1.4 via OTA prior to installing OTA updates for iOS 9.0 or newer. An exception to this is iOS 6.0 on the iPhone 5.

Users still on iOS 7.1 through 7.1.2 may update to iOS 9.0, but appear to be given a dummy update first.

iPhone 4S
Users still on iOS 5.0 or 5.0.1 must update to 6.1.3 via OTA prior to installing OTA updates for iOS 8.0 or newer.