nReach has announced a Bluetooth adapter for the Game Boy Advance, which will let you play GBA games against someone else wirelessly.
The nReach Bluetooth Adapter lets GBA users play games, send and receive Instant Messages, and access channel-based Internet content. A GBA user can use the Bluetooth adapter to connect to the Internet through their PC via a Bluetooth USB adapter, through a Bluetooth enabled cell phone, person to person, or through an nReach deployed "Hot Spot". These nReach "Hot Spot" environments are being deployed by various retailers, malls, and other commercial locations.
The Bluetooth Adapter for the GBA will be available in Q2 of 2002.