I don't have a lot of information on this, all I know if that Nintendo offered this modem for use with some sort of online banking service they were involved with at the time. There were no head-to-head modem games, as far as I know. I assume, but am not positive, that those little TG16/PC Engine-like cards were used to store data, and possibly contained programs (like the FC version of Popeye?). If you have more info, please send it in.

Pic ripped from eBay