Everything 802.11b/g
UPDATE: MacRumors also found remote file access for MobileMe users:
Access files on a networked drive from anywhere - Allows MobileMe subscribers to register their AirPort Express Base Station or
Since all current and previous iPhone (and iPod touch) devices have 802.11b/g WiFi, if placed on a faster, wider-range 802.11n network, they typically cause such networks to downgrade to 802.11b/g
