It seems that a new bug discovered on Windows Phone 7.5 Mango will allow users to crash your Messaging Hub if they send you an SMS from another Windows Phone, and by including a specific string of text within the message. Since the Messaging Hub also compiles chats from Windows Live Messenger and even Facebook Chat, this bug could also be triggered by any of these messaging services as long as the adequate string of text is used.
According to the source: The flaw works simply by sending an SMS to a Windows Phone user. If the SMS contains a particular string of text then Windows Phone 7.5 devices will reboot and the messaging hub will not open despite repeat attempts. We have tested the attack on a range of Windows Phone devices, including HTC’s TITAN and Samsung’s Focus Flash. The attack is not device specific and appears to be an issue with the way the Windows Phone messaging hub handles particular characters. The bug is also triggered if a user sends a Facebook chat message or Windows Live Messenger message to a recipient.
This goes as bad as to even having your phone crash over a friend posting this string of text on their Facebook page if you’ve created a Live Tile for that specific friend.
We haven’t personally tested this, since we obviously don’t want any of our Windows Phones to become unusable, but leave ac moment down bellow if you’re experiencing this problem.