If you are already a Hotmail user, you can join in this initiative.
It just puts the i’m-specific advertisement at the end of your emails.
So how to activate it?
Signin to your Hotmail, Go to 'options' at the top right, below
the signout link, Click on the 'more options' and you can find it
under the 'Customize your mail' .From there you'll get a page to select the cause of your choice. That's
all. So whenever you send an email, it'll put an i'm specific ad. Check the screenshots at Hotmail users can also join i'm Initiative
This is again US specific.