Hihi. Long time no see, etc. etc.

I'm looking at the Bulbapedia aritcle on Oak's Letter ( http://bulbapedia.bulbagarden.net/wiki/Oak%27s_Letter ) and it says "It was released over Nintendo Wi-Fi for the first time from April 18 to May 11, 2009 for players of the Japanese version of Platinum."

Now, I happen to have a Japanese version of Platinum. It happens to be between April 18 and May 11 2009. I even happen to be in Japan. But I'm still bamboozled as to how one should get the letter in question from this mysterious "Wi-Fi". Is it some function of the Global Terminal?

An explanation would very much be appreciated.

Thank you all in advance.