Those that download the PokeBank app now will receive a free Celebi after they deposit their first Pokemon. The app is available on a free trial from now until March 14.
To download the app, the Nintendo 3DS system must be up to date. It should be easily found in the eShop. In order to retrieve Pokemon from older games fans must also download the PokeTransporter app.
Interestingly the release of the PokeBank app has yet to be announced on social media by either Pokemon or Nintendo of Europe. The reasoning for this could be so that the servers aren't overloaded all at once, which is one of the reasons the app was delayed to begin with.
There is still no word on when PokeBank will see an American release. Stay tuned for that information as it comes along.