Instructions
Click the "Wii Message Board" icon in the lower right-hand corner of your Wii load screen. The icon has a picture of a small envelope on it.
Press the "Create Message" button on the left-hand side of the screen. This icon looks like a pencil and paper.
Open your "Address Book." It is clearly labeled on the right-hand side of the screen.
Copy the 16-digit "Wii Number" located in the address book. This is the number that identifies your Wii console. If you have already added "Wii Numbers" to your console, you will have to press the flashing arrow on the left side of the screen to go back to the first page of your address book, where your code is listed.
Exchange your Wii number with friends. This will allow you to send messages or gifts to your friends.