The Japanese 7-Eleven website announced a Pokémon Event distribution.
This Pikachu will be be available in 15 stores located in Tokyo. It will be distributed from August 20, 2010 to September 5, 2010. Of course all games DPt and HGSS can recieve it.
I, myself, have no idea if this will unlock any event in BW or if it's just an event.
Source:
http://www.sej.co.jp/cmp/wifi1007.html