This entry refers to the Game Boy Micro portable console. Since the console is not region locked, this encompasses all regions in which it was sold.
From Wikipedia:
The third form of Game Boy Advance system, the Game Boy Micro is four inches wide (10 cm), two inches tall (5 cm), and weighs 2.8 ounces (80g). By far the smallest Game Boy created, it is approximately the same dimensions as an original NES controller pad. Its screen is approximately 2/3 the size of the SP and GBA screens while maintaining the same resolution (240×160 pixels) but now has a higher quality (than original SP, not improved SP) backlit display with adjustable brightness. In the United States and Canada, except for the 20th Anniversary Limited Edition Game Boy Micro (pictured on the left), included with the system are two additional faceplates which can be swapped to give the system a new look; Nintendo of America sells additional faceplates on its online store. In Europe, the Game Boy Micro comes with a single faceplate. In Japan, a special Mother 3 limited edition Game Boy Micro was released with the game in the Mother 3 Deluxe Box. The Game Boy Micro is unable to play any original Game Boy or Game Boy Color games, only playing Game Boy Advance titles (with the exception of the Nintendo e-Reader, discontinued in America, but still available in Japan).