The Nortel UNIStim IP Phone appears to suffer from a spoofing vulnerability that allows for message interception.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/60257/ipphonesurveil-spoof.txt
Source: https://packetstormsecurity.com/files/60257/ipphonesurveil-spoof.txt.html