The UIKit Alerts component in Apple iOS before 5 allows remote attackers to cause a denial of service (device hang) via a long tel: URL that triggers a large size for the acceptance dialog.
https://exchange.xforce.ibmcloud.com/vulnerabilities/70561
http://support.apple.com/kb/HT4999
http://lists.apple.com/archives/Security-announce/2011//Oct/msg00001.html