Federal officials and leaders of the nation's largest wireless telephone companies are set to announce ... that they're launching a new mobile telephone emergency alert system by the end of the year in Washington and New York. The Personal Localized Alerting Network, or PLAN, won't be available across the rest of the country until April, but top executives from AT&T, Sprint, T-Mobile and Verizon are scheduled to join Federal Communications Commission. Authorities plan to continue broadcasting messages across the Emergency Alert System on radio and television. Mobile users who currently own or plan to buy newer smart phones and cell phones sold by the four wireless companies would be able to receive the free, text-like messages that would flash across a telephone's screen and trigger a special vibration. Once operational, participating federal, state and local agencies would be able to send information regarding only the most serious alerts - including warnings about natural disasters, terrorist attacks or AMBER Alerts.