Today, at 2:18pm EDT (happened at 2:19pm for me), there was a rare test that happened on all cell phones (even on mine).
The message was;
EMERGENCY ALERTS
Presidential Alert
THIS IS A TEST of the National Wireless
Emergency Alert System. No
action is needed.
(This also came with the familiar alert tone that you typically hear on a TV, or a radio)
The test was conducted by FEMA (not the President himself), as a new way to (just incase) warn of a large-scale threat heading to America (such as a chemical attack, a nuke, or even a zombie invasion). It also has typical weather alerts that affect life and property (like a Tornado Warning).
And of course, Twitter (and other social media platform users) are tearing it apart and turning it into memes.