It is very possible!
PokeBank is a Nintendo 3DS app that is on the eShop. It costs AUD$4.99 per month, and it comes with PokeTransfer.
PokeBank is basically a huge storage system, like a PC, except extended.
PokeTransfer is a system that transfers Pokemon from Black, White, Black 2 and White 2 into X and Y.
Hope I helped. :)