The Pokémon Company and Niantic invite users to field test Pokémon GO in the United States of America. Users can visit http://pokemongo.nianticlabs.com to sign up. Please note that sign up doesn’t guarantee access to the field test. The Pokémon GO field test will give users the opportunity to share early feedback and help improve the Pokémon GO experience.
Thank you for your interest in Pokémon GO.
— The Pokémon GO Development Team