Mobile app monetization and distribution network W3i is announcing the results of its tests to determine whether or not an iPhone's MAC address can serve as a replacement to the UDID (the unique device identifier), which Apple is phasing out as a way for developers to track an app's users. According to W3i, developers can and should begin tracking the iPhone's MAC address as a UDID alternative, as it has successfully seen Apple approve its own application where this is the case.