Wireless Telephone Number Portability Act of 2003 - Directs the Federal Communications Commission to require each wireless telephone service provider offering service in one of the largest 100 U.S. metropolitan statistical areas to provide consumers with the option to port (retain) telephone numbers between providers by implementing wireless telephone number portability throughout the networks of providers in each of those statistical areas. Mandates subsequent implementation of such requirement with respect to all other metropolitan statistical areas in which three or more providers provide wireless service.