Nintendo recently sent us the final US Game Boy Advance hardware, along with copies of two of the system's launch games: Super Mario Advance and F-Zero Maximum Velocity.
In truth, the territory change hasn't affected the system in the slightest. Cosmetically, it looks identical to the Japanese units we've had for a while, and it's functionality is similarly unchanged. The US unit's back label, however, makes no reference to the rechargeable battery pack that Nintendo plans to market for the system in Japan (which is referred to as NiHM AGB-003 on the Japanese unit). This could be construed as evidence that Nintendo doesn't plan to market the peripheral in the US. There has been no official word on the matter, though, so it is still a possibility.
Both of the games that Nintendo shipped along with the unit are effectively identical to their Japanese counterparts, barring the translation of the menu and some of the accompanying sound bites. In Super Mario Advance, Super Mario Bros. 2 is referred to by its proper US name, rather than "Super Mario USA," as was the case with the Japanese version.
Multiplayer games between US and Japanese units seem to work perfectly. Single-cart games of both F-Zero and Super Mario Advance worked normally, as did dual-cart games of F-Zero.
We can also finally confirm that Japanese games will work in US units and vice versa. This should dispel many peoples' misgivings regarding importing the system.
The Game Boy Advance is set to release in the US on June 11.