The packet-storing feature on Cisco 9900 phones with firmware 9.3(2) does not properly support the RTP protocol, which allows remote attackers to cause a denial of service (device hang) by sending malformed RTP packets after a call is answered, aka Bug ID CSCur39976.
http://www.securitytracker.com/id/1032748
http://www.securityfocus.com/bid/75471
http://tools.cisco.com/security/center/viewAlert.x?alertId=39554