I remember the Game Boy radio player accessory and even later the official Nintendo MP3 player which was a Japan exclusive for the GBA (if I remember correctly). This is a third party MP3 player accessory. I've never seen it before.

http://www.ebay.com/itm/152048662...

You should update the title to include "Advance". I was definitely like wtf, an MP3 accessory for the original Game Boy doesn't even make sense.

This was supposed to come out originally for GBC, but I'm not sure if it did. There was a member on here a little wile back that had one or a demo unit that I was interested in. I remember wanting one way back when.

It works on Game Boy Color? Whaaaat?

The auction says it works with GBC. From the pictures, the cartridge slot adapter looks like it would fit even in an original Game Boy; however, I'm sure the programmers put some checks to determine if the software was being booted on anything before a GBC.
 

oh, you seem to be right. haha that's crazy.

I never knew such an accessory existed.

All this fancy new technology , next thing your going to tell me that all my records and tapes are obsolete

It's cool not $100 cool though, I'd definitely seem $40 or so on it.