If your actual handset is an Android-based smartphone, you might have already received some strange SMS messages containing numbers. These messages are CB messages which stand for Cell Broadcast messages.
Cell Broadcast is a technology which has been developed to address the largest number of people in emergency cases for instance regardless of the mobile operator.
To (des)activate it, the option can be found in the “messages settings” and then “CB messages” option can be found. The way you can modify it depends on your smartphone model and on your Android OS version.
More about Cell Broadcast : Wikipedia Cell Broadcast page