Linking the Wonderswan to PS2 to upload saves and data exchange with Bandai-only games. I found out that this feature was also related to SD Gundam G Generation games on PS. By connecting and swapping, you get extras unlocked only through acquiring their counterparts on the other console.
Odd and strange gadgets that can only be found in Japan:
A feature offered in many early Japanese GBA games, this option allowed players to connect through their keitai units and share scores or play against each other. At the time this feature was included in the GBA games, the cellular industry was still in the experimental stage of toying around with many ideas for keitai futuristic technologies. The service is offered only in Japan and I think it also falls under which phone operator you’re using and I don’t know if its still running. I think it’s abandoned right now, since the inclusion of Wi-Fi in NDS.
Exactly the same as Mobile System GB for GBA, Bandai thought about this link before Nintendo did. As apparent from the image, the phone looks pretty old, so I guess this was around late 90′s or early 2000. Used to upload game scores, check stats and other related data.