I saw a thread on this, but there was no final answer and it was 4 years old. I have an r4 card, a dsi and a 3ds xl. I'd like to put the r4 into the 3ds and have it communicate with the ds using pictochat. If I remember,I thought I could access pictochat from the r4 but maybe it was a game. I read there is an .nds bios file or something that is just pictochat to put on there. I've also read there are a few games that have it-specifically a Japanese game but u have to know how to read...
R4 pictochat
R4 pictochat