Mayor Michael Bloomberg joined federal officials at Ground Zero Tuesday to unveil a system that will allow wireless customers to receive messages alerting them of imminent safety threats in their area.

The Personal Localized Alerting Network, or PLAN, is a free service that sends geographically targeted, text message-like alerts. The messages — which include alerts issued by the president, alerts involving imminent threats to safety of life and Amber Alerts — are sent by authorized government officials and are pushed out by participating wireless providers using their cell towers.

According to the Federal Emergency Management Agency (FEMA), the alerts will not get stalled by user congestion. Carriers may allow subscribers to block all but presidential alerts.

Phones must be outfitted with a special chip — already included in some smartphones, such as the latest iPhone — and undergo a software upgrade to receive the messages, The New York Times reported.

“Given the kinds of threats made against New York City at the World Trade Center, Times Square, and other places popular with visitors and tourists, we’ll be even safer when authorities can broadcast warnings to everyone in a geographic area regardless of where they came from or bought their phone,” Bloomberg said in a statement announcing the new system.

FEMA Administrator Craig Fugate said in the statement that the technology “could become a lifeline for millions of Americans and is another tool that will strengthen our nation’s resilience against all hazards.”

PLAN will be available in New York City and Washington, D.C., by the end of 2011, and the system will continue to expand to other areas throughout next year.

Congress passed legislation in 2006 requiring wireless carriers that choose to participate to activate PLAN technology by April 2012.