The 3DS Miiverse won't allow private messages or friend requests
Likely due to Friend Codes already existing.
Earlier this week Nintendo announced that it's bringing its Wii U social network Miiverse onto the 3DS in December. Unfortunately, it's just been revealed that the 3DS implementation of the service won't allows private messages or friend requests.
A Nintendo rep confirmed the omitted features in a comment to NintendoLife, bluntly stating: "Miiverse on Nintendo 3DS does not include friend request or user messaging features."
Ostensibly this is because the 3DS already has its own variant of these features with its Friend Code system used for adding mates, while messages/pictures could be sent to your pals via Letter Box. [Editor's Note: Though Nintendo just disabled this feature two weeks ago due to 'offensive material.']
Still, players will be able to use the Miiverse to consolidate their eShop balances between both Nintendo platforms' digital storefronts, and they'll be able to leave comments and drawings about a particular game in the Miiverse's bulletin-board like setup.
There's no telling if the missing features will be added at a later date, but we're looking into it.