For most American 3DS owners, obtaining new StreePass data can be a challenge. Nintendo’s solution to this is the brand new Relay Point system.
After updating to the latest firmware, 3DS owners can connect with other 3DS users via Nintendo Zone locations. How it works is simple: walk by a 3DS Relay Point with your 3DS in sleep mode (just close the lid while the power is on). You information will then be dropped off at this Relay Point while picking up the data of the previous Relay Point goer. Relay Points can be found all over America in places like BestBuy, Simon Malls, McDonalds, Starbucks, and even AT&T Wi-Fi Hot Spots.
It is only possible to get one user’s SteetPass data this way as the Relay Points does not retain the data for all users; one person’s data goes in, one person’s data goes out. Also, if you are the very first user of a Relay Point, you will obviously not swap data with anyone but yours will be dropped off.
SteetPass is used to unlock additional features in games like Super Mario 3D Land, Animal Crossing New Leaf, or Fire Emblem Awakening. Most importantly, SteetPass data adds puzzle pieces and other goodies in the SteetPass Mii Plaza.
More information can be found here.