The Old Skool 4 Player Link Cable is compatible with the Game Boy Advance and Game Boy Advance SP, and allows you to play multiplayer, as well as to transfer date with other Game Boy Advance and Game Boy Advance Sp systems.  With the Old Skool 4 Player Link Cable you can connect up to 4 systems simultaneously.
Compatible with Game Boy Advance and Game Boy Advance SP
Connect up to 4 GBA / GBA SP systems
Cable length of 5ft
Transfers date between systems