Nintendo and The Pokemon Company International have released a statement informing the public that the western releases of both the Pokemon Bank and the Poke Transporter will see delays due to the large amount of traffic plaguing the Nintendo Network service at this time. The number of users attempting to access the Network in recent weeks has caused a bottleneck clog of sorts, preventing people from setting up their Network IDs and even from downloading content.
These apps were originally intended to be launched today, December 27th. As a result of this delay, there is no word as to when the two accompanying Pokemon apps will see a western release. The two apps–as one could surmise from their names–have to do with the cloud storage and transfer of captured Pokemon between titles. The Poke Bank allows players to upload their captured Pokemon for storage, and the Poke Transfer.
Source: Nintendo Support.