Important Friend Code Thread

On a 3DS you can usually meet people via Streetpass if you and another person with a 3DS happen to be passing by at the same location. Spotpass is usually used for news and updates by Nintendo or interactions between friends on your Friend List.
One example for Spotpass is the Nintendo Swapdoodle (formerly known as Nintendo Swapnote) App where you can send drawn messages to your friends via Spotpass. Another example is like already mentioned exchanging Profile Cards in Project Mirai DX and PV comments, jingles etc.
The more Profile Cards you collect, the more collectible stamps you get.

See:
http://projectdiva.wiki/Stamps (Mirai DX)

[xtable=652x@]
{tbody}
{tr}
{td=21x@}101{/td}
{td=88x@}Beginner{/td}
{td=228x@}Prepare to have people get to know you.{/td}
{td=268x@}Set up your profile card{/td}
{/tr}
{tr}
{td=21x@}102{/td}
{td=88x@}First Contact{/td}
{td=228x@}Have someone get to know you.{/td}
{td=268x@}Send your profile card to other players (via Spotpass/Streetpass){/td}
{/tr}
{tr}
{td=21x@}103{/td}
{td=88x@}Messenger{/td}
{td=228x@}Get to know some people.{/td}
{td=268x@}Receive 20 cards from others (50 in Mirai 2){/td}
{/tr}
{tr}
{td=21x@}104{/td}
{td=88x@}Social Butterfly{/td}
{td=228x@}Get to know a lot of people.{/td}
{td=268x@}Receive 50 cards from others (100 in Mirai 2){/td}
{/tr}
{tr}
{td=21x@}105{/td}
{td=88x@}Charmer{/td}
{td=228x@}Fill up your card case.{/td}
{td=268x@}Receive 100 cards from others (200 in Mirai 2){/td}
{/tr}
{/tbody}
[/xtable]