A version of the iPhone for Sprint is in advanced testing, according to a new report. Citing anonymous sources, 9 to 5 Mac reports that the physical design of the device is similar to the current iPhone 4, leading them to believe that the device might be the so-called iPhone 4S with support for all carriers. The report also states that Apple ordered Sprint-compatible cell towers for on-campus testing in late 2010, and that the device is also “making the rounds” among members of Sprint’s research and development department. Notably, the report also states that the Sprint-compatible iPhone currently in testing is not compatible with the carrier’s 4G network. A recent Apple job posting for a Carrier Engineer in Kansas City, MO—close to Sprint’s headquarters—suggested that Apple may be planning to offer a version of the iPhone on Sprint, lending credence to this latest report.