Pingtel xpressa SIP-based voice-over-IP phone 1.2.5 through 1.2.7.4 allows attackers with physical access to restore the phone to factory defaults without authentication via a menu option, which sets the administrator password to null.
http://www.pingtel.com/PingtelAtStakeAdvisoryResponse.jsp
http://www.iss.net/security_center/static/9567.php
http://www.atstake.com/research/advisories/2002/a071202-1.txt