The Thomson ST 2030 SIP phone with software 1.52.1 allows remote attackers to cause a denial of service (device hang) via (1) an empty SIP message or (2) a SIP INVITE message with a malformed To header, different vectors than CVE-2007-4553.
https://exchange.xforce.ibmcloud.com/vulnerabilities/36286
http://securitytracker.com/id?1018616
http://securitytracker.com/id?1018611
http://securityreason.com/securityalert/3104
http://secunia.com/advisories/26587
http://lists.grok.org.uk/pipermail/full-disclosure/2007-August/065478.html
http://lists.grok.org.uk/pipermail/full-disclosure/2007-August/065458.html