iDownloadblog reveals some new iOS 5.1 strings that include references to "4G".
“4G_ON_CALL_CANCEL” = “Cancel”;
“4G_ON_CALL_OK_DISABLE” = “Disable”;
“4G_ON_CALL_OK_ENABLE” = “Enable”;
“4G_ON_CALL_WARNING_DISABLE” = “Disabling 4G will end your phone call. Are you sure you want to disable 4G?”;
“4G_ON_CALL_WARNING_ENABLE” = “Enabling 4G will end your phone call. Are you sure you want to enable 4G?”;
“4G_ON_FACETIME_4G_WARNING_DISABLE” = “Disabling 4G will end FaceTime. Are you sure you want to disable 4G?”;
“4G_ON_FACETIME_WIFI_WARNING_DISABLE” = “Disabling 4G may end FaceTime. Are you sure you want to disable 4G?”;
“4G_TEXT” = “Using 4G loads data faster, but may decrease battery life.”;
The site suggests these may have been put in place for true 4G ("LTE") in the next iPhone.
While we do believe the next iPhone is likely to get LTE, our guess is that these 4G strings were put in place at the same time to reference the updated 4G indicator that Apple also included in the iOS 5.1 update. Existing iPhones now show "4G" at the top of their screen when they are on AT&T's HSDPA+ network. We expect Apple will continue to distinguish the faster LTE networks by specifically calling them "LTE" as they do on the 3rd Generation iPad.
We also don't think references to 4G and Facetime are necessarily predictive. Apple has had strings in the past suggesting that Facetime might work under cellular data, but the restriction appears to be carrier imposed rather than a technical issue.