With the introduction of a new LTE iPad, there is no shortage of rumors about a 4G iPhone not being far behind. We saw LTE in iOS code strings before the new Pad was introduced, but it was only speculation whether those were for iPhone, the new 4G iPad, or both.
Today, code strings in iOS 5.1 discovered by Cydia developer Krishna Sagar contain the text: “Enabling 4G will end your phone call. Are you sure you want to enable 4G?” It also has various other mentions of enabling and disabling 4G when on phone calls and FaceTime. While most of the references to 4G in the strings could be for the iPad, references to calling features is pretty solid evidence that Apple is at the very least testing a LTE iPhone.
AT&T recently began calling its HSPA+ service 4G on iPhone 4S, but switching that on and off would not disable a phone call or a FaceTime chat.
There is also a full reference to FaceTime over 4G in the code strings (below):