Update: MAC address quire is depreciated since iOS 7.
In iOS 7 and later, if you ask for the MAC address of an iOS device, the system returns the value 02:00:00:00:00:00. If you need to identify the device, use the identifierForVendor  property of UIDevice instead. (Apps that need an identifier for their own advertising purposes should consider using the advertisingIdentifier  property of ASIdentifierManager instead.)