The Telephony subsystem in Apple iOS before 7 does not require API conformity for access to telephony-daemon interfaces, which allows attackers to bypass intended restrictions on phone calls via a crafted app that sends direct requests to the daemon.
http://www.securitytracker.com/id/1029054
http://support.apple.com/kb/HT5934
http://secunia.com/advisories/54886
http://lists.apple.com/archives/security-announce/2013/Sep/msg00006.html