This just in from Notify NYC:
Tomorrow between 10AM-3PM, New York City OEM and the federal government (FEMA) will test the Wireless Emergency Alert System, a new system that allows authorized officials to send alerts to enabled mobile phones. Depending on the model of your phone and carrier you may receive TEST messages. These messages will look similar to a text message and be accompanied by audible alerts. For more info see attached, or contact your mobile service provider.
The attachment is here.