In another sign that the FCC is stepping up its vigilance against potentially anticompetitive practices that involve the nation’s wireless phone carriers, the agency delivered letters to Apple, Inc., AT&T and Google that seek information on Apple’s recent decision to reject the Google Voice application for the iPhone. Like Skype’s popular calling software, Google’s web-based application enables users to place low-cost international and free calls and thus competes directly against the wireless voice offerings of AT&T—the exclusive U.S. retailer of the Apple iPhone. Although the letters mailed last Friday are not viewed as the prelude to a formal investigation, the inquiry is said to be related to the FCC’s continuing probe into exclusive deals between handset makers and major mobile phone operators that include Verizon Wireless and AT&T. Among other things, the FCC asked Apple to explain its rejection of the Google Voice application and its related decision to remove Google Voice from the iPhone application store. Separately, the agency asked AT&T what role, if any, it played in Apple’s decision. Google, meanwhile, was asked to detail how its voice application would operate on the iPhone and if Apple offered any explanation as to why that application was rejected. The companies are required to respond to the FCC’s inquiry by August 21. Asserting that the FCC “has a mission to foster a competitive wireless marketplace,” FCC Chairman Julius Genachowski said the letters “reflect the Commission’s proactive approach to getting the facts and data necessary to make the best policy decisions.” While Apple declined to comment on the matter, an AT&T spokesman stressed that his company does not “manage or approve” applications in the iPhone store. Promising to “supply the information that the Commission has requested,” Google pledged to “continue to work to bring our services to iPhone users, for example by taking advantage of advances in mobile browsers.”