Joining online friends
If your Nintendo 3DS has system software version 2.2.0-(4, 3, 2, 1, 0)E or higher, you can see which games your online friends are playing. You can even join your friend's game if the corresponding game supports it, and if you have the same Game Card inserted. To do this, simply bring up their friend card and tap Join Friend's Game.
If you have an older system software version, please perform a system update to get the latest version available. Click here for more information about performing system updates on your Nintendo 3DS.