They are unique codes generated by your WiFi enabled game and your DS.
By adding people’s friends code to your Friends Roster and them adding
you to theirs, you will be able to visit their towns when they are
online and they will be able to visit yours.
How do I get my friend code?
get your Friend Code, visit the checkpoint located at the north end of
your town and talk to Copper. When asked, let him know you want to set
up a Nintendo WFC connection. He will let you know that you do not yet
have a Friend Code and then issue one to you.
My Friend Code for Animal Crossing is 081759115116.
What do I need?
A high-speed internet connection (Cable or DSL).
A wireless router or Nintendo’s Wi-Fi USB Connector
Full connection information can be found here:
How do I add a friend to my Friends Roster?
add a code to your Friends Roster, tap the "up" arrow in the upper
right-hand corner of the screen, and then tap the heart icon. On the
following screen, tap "Register" and then enter the Friend Code you
received from the player you wish to visit or invite to your town.
How do I receive the Nintendo letters?
Nintendo will send out communications to all Animal Crossing Wild World
players. These can be messages from game designers, Nintendo Power
staff, and even the president of Nintendo himself. Letters may also
contain exclusive items that can’t be obtained anywhere else in the
If you wish to receive letters and other communications
that Nintendo sends out to Animal Crossing Wild World players, pick up
the phone in your character’s bedroom and select ‘Downloads.’ Tap
through the dialogue until you are asked, "What about downloading
letters and bulletin board messages?’, and select "That’s fine."