The Telephony component in Apple iPhone OS before 3.1 does not properly handle SMS arrival notifications, which allows remote attackers to cause a denial of service (NULL pointer dereference and service interruption) via a crafted SMS message.
http://support.apple.com/kb/HT3860
http://secunia.com/advisories/36677
http://lists.apple.com/archives/security-announce/2009/Sep/msg00001.html