AT&T is planning to promote the iPhone 4S as a “4G” device in an effort to differentiate itself from rival carriers Verizon and Sprint, according to a new report. Citing a internal an internal memo that has since been confirmed by AT&T, The Verge reports that the company is working with Apple to have “4G” branding added to the status bar of iPhone 4S devices running on its network. While both AT&T and T-Mobile have…