On Thursday, FEMA will conduct a test of IPAWS: Integrated Public Alert and Warning System. It will send a message to all the phones in the US to test the infrastructure of the warning system. The test will happen around 2:18 PM ET and will last a half hour.
Rich says it's a big deal that the federal government will take command of every cell phone tower in the country in order to reach everyone at once with a test emergency text message. Rich also says that while there is an opt out provision for some emergency alerts, this isn't one of them. You cannot disable it.