So, at WLM’s blog they explained about the new emoticon:

note: currently the donation only applies to Windows Live Messenger users in the United States. If you are in the US and you are IMing with a contact in another country your IM activity will be counted towards the donation.

Wonderful! How does it work?

1. Use Messenger 8.1
2. Add the i’m emoticon to your display name by entering the code of the cause you would like to support (hint: I suggest adding it at the end of your name so you still appear in the correct alphabetic order in your contacts list)
3. Send and receive IMs
4. A portion of the advertising revenue generated by your usage of Messenger will be donated to your cause. So the more IMs you send and receive the more money will be donated to your cause.

What does the i’m emoticon represent?

It tells your contacts that you are making a difference, it is short for “i’m making a difference”.

What are the i’m emoticon codes and causes?

American Red Cross –  ready to help, code = *red+u
Boys & Girls Clubs of America —  providing a positive place for kids, code = *bgca
National AIDS Fund —  fighting AIDS, code = *naf
National MS Society —  joining the MS movement, code = *mssoc

ninemillion.org —  helping 9 million refugee kids, code = *9mil
Sierra Club —  exploring and protecting the planet, code = *sierra
StopGlobalWarming.org —  stopping global warming, code = *help
Susan G. Komen for the Cure —  finding the cure, code = *komen
UNICEF —  helping kids survive, code = *unicef

Read more at messengersays.spaces.live.com.