Nintendo have confirmed that their Pokémon Bank and Poké Transporter applications will release across North America on December 27th.
The service will provide you with 100 Boxes that can each store 30 Pokémon, which amounts to space for 3,000 Pokémon in total. Coupled with the Poké Transporter companion software, this allows you to shift your captured Pokémon from either Black, White, Black 2, White 2, X or Y to your online storage.
Pokémon Bank and Poké Transporter will release across North America on December 27th, the same day as in Europe, with Japan getting it slightly earlier on December 25th.