Happy days are here:
Sega Mega Modem and Mega Answer Ten Key Pad!
So after I managed to snag the Mega CD Karaoke unit awhile back, I figured I might as well go full bore crazy when it comes to the MegaDrive accessories. It took awhile of looking at auctions in Japan that weren't overpriced but eventually a seller appeared with both a Mega Modem and the 10-key starting at about $10 each, I won both of these pretty close to that and then shipped them right over along with a couple other things!
The Mega Modem goes on the back of the Genesis and uses the EXT port, and even comes with a screw to help hold it place similarly to the Power Base Converter. The Ten Key Pad has a regular Genesis/DB9 connector on the end and plugs into the controller ports of the Mega drive.
There are a couple ways the modem itself was released: standalone, bundled with games, or like the bundle I have now which was with a package called the MegaAnswer which was used with a Japanese bank. To my understanding, the rest of the MegaAnswer system involved a printer if you wanted to print receipts, and a custom cartridge that was used to connect to the bank in question. Then you would use the custom 10-key controller to navigate their bank system on your home MegaDrive. By the way, there are actually more than 10 keys on the pad. It gets its name from the 10 numeric keys on it like a regular office 10 key pad.