Ars Technica reported a week ago that there was a flaw in iMessage, Apple's iOS 5 alternative to sending traditional MMS and Text messages. They noticed that any lost or stolen iPhone could continue to receive iMessages directed towards your cell phone number—even if you remotely wiped the iPhone’s data, moved your number to a new phone, or changed your Apple ID’s password.
How to fix this issue ? Two things can be done for solving this issue. The first thing that you can do is to switch on the iPhone's SIM PIN.
What will that do? Well a SIM PIN is not the same as your iPhone's PIN. It locks the actual SIM card and this would mean every time you switch on your iPhone, you have to enter the code. The Verizon customers can't do this as they don't have a pin to lock and as pointed out by MacWorld, setting the PIN for Verizon handsets might lead to problems rather than solving the issue.
The far simpler solution—and the one that doesn’t leave Verizon customers in the lurch—is to go through that three-stop process mentioned above: Wipe your old phone, tell your carrier to deactivate its SIM, and then activate your new SIM. Since SIM PINs are not without risk, and entering the code whenever your iPhone reboots is an added annoyance, remembering the three-step workaround seems like the way to go.I think the second one is easier than the first one! Let's just hope we don't have to go through such situation!
(source: Arc Tehnicha)