The Zyxel P2000W (Version 2) VoIP wireless phone has an undocumented port, UDP/9090, that provides an unauthenticated attacker information about the phone, specifically the phone’s MAC address and software version.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/43264/ZyXelP2000W.txt
Source: https://packetstormsecurity.com/files/43264/ZyXelP2000W.txt.html