Letter
From Wild World Wiki
Letters are an excellent way to communicate with other people in AC:WW. To write a letter, you must have paper to write it on. You can send letters to anyone currently in your town, whether they be NPC resident or human character. However, you cannot send letters to the non-resident NPCs (examples being Tortimer the mayor or K.K. Slider). You can also recieve letters from all residents and human players, as well as the H.R.A., your Mom, and residents of towns you have visited over wifi.
[edit] Presents
It is possible to send a recieve presents using letters. To send a present, choose the item you wish to send and drag and drop it over a pre-written letter to the person you want to recieve the gift. When the person recieves the letter it will be marked as having a present. Removing the present will put it in their inventory.