In theory, this should be possible even for those using real cartridges instead of flashcarts. Using my modded dsi, I extracted the save files from my 2 DQIX cartridges (it was easy to do), loaded them both into a melonds window, and they could communicate just fine in game on the emulator. There's a way to put these save files back onto their cartridges, and while I didn't personally try it I don't see any reason why it wouldn't work.
Hi, I'm the guy who made the original topic/guide. Got a tip from someone that this thread existed and I thought I'd stop by. Basically, all you need to do is change the DNS in the DS wifi settings to either 126.96.36.199 or 188.8.131.52. The annoying thing is that as you may know, the DS doesn't support most modern networks. I have 5 different ways of getting around this, and some of them work for different people. 1. Tether an older router to your main router and connect your DS to it 2. Make an open hotspot on an Android Phone 3. Use the Nintendo Wifi US