Cisco IP Phone (VoIP) models 7910, 7940, and 7960 use a default administrative password, which allows attackers with physical access to the phone to modify the configuration settings.
http://www.securityfocus.com/bid/4799
http://www.iss.net/security_center/static/9144.php
http://www.cisco.com/warp/public/707/multiple-ip-phone-vulnerabilities-pub.shtml