don()shinobi, Yes... No...
There's SwapNote, but it's not instant. Then there's the Best Friend function in New Leaf, where if you've both added each other (if you're in a town together you just tap the "Visitors" button, then the heart beside their name to add) you can instant message if you're both in-game and both have the Best Friend Message feature turned on.
So yeah, there's ways to message, but nothing simple unfortunately...