Nintendo's Game Boy Advance Wireless Adapter, which allows for cordless multiplayer gaming between GBA owners, was previously available with Pokemon FireRed and Pokemon LeafGreen, but it's now sold separately for $20. The adapter plugs into the same specialized port on top of the original GBA and the GBA SP that accommodates the standard link cable. Because the Game Boy Micro lacks that port, this adapter is not compatible with it, though Nintendo offers a special Game Boy Micro Wireless Adapter through its site for the same price.
The device is pretty small and unobtrusive--it's roughly the same size as a GBA cartridge, and the clear grey color works well with the myriad designs for the portable. The biggest problem is the dearth of titles available for the device. Fewer than 20 titles are compatible, and just 3 games are enhanced by employing the adapters--the aforementioned Pokemon titles, as well as Pokemon Emerald allow as many as 16 players to play together.
Using the adapter among that small group is a bit tricky, as there are multiple ways for the games to recognize the device. Some will play as if the adapter is a link cable, while others require the adapter's internal menu to recognize the title first. Nintendo recommends you check the game's instruction manual to determine the correct method, but the portable nature of the system and its games often make finding a title's documentation a bit of a hassle. The system's compatibility problems were most evident when playing the Classic NES series titles. We booted up Super Mario Brothers, which features single-cart multiplayer, only to be dismayed when the second, cartless GBA wouldn't recognize it. Only after scanning Nintendo's troubleshooting page did we find the solution: the main player had to hold down the left and right shoulder buttons to bring up a special menu.
When we got the game up and running, the gameplay experience was pretty smooth. There was some slight lag at the beginning, but it evened out as long as the systems were within reasonably close proximity. Nintendo recommends that systems remain within 10 feet of each other, but we were able separate them by about 40 feet before the lag reappeared, and by 50 feet before they lost contact.
Ultimately, the Nintendo Game Boy Advance Wireless Adapter would be a worthwhile device if it had the same compatibility as the system's link cable, which works with every multiplayer game. As it is, it's worth picking up only if you own a good percentage of the games compatible with the device.