WASHINGTON, DC - The U.S. Postal Service announced today that First-Class letters are beginning to take to the air via commercial airliners. It also announced that a toll-free number is now available to assist Manhattan residents and businesses obtain their mail -- including businesses that were located within the World Trade Centers. For all residential and small business customers served by the Bowling Green, Wall Street and Church Street Post Offices, mail pick-up service is available at 380 West 33rd Street between 8th and 9th Avenues in the General Post Office's (Farley Building) side lobby. Business mailers that receive large volumes of mail can pick up this mail 24-hours-a-day, seven-day-a-week at West 31st Street between 8th and 9th Avenues, truck bays 15-17. All other customers may obtain their mail Monday through Saturday, 7 a.m. to 4 p.m. Post Office Box holders can pick up mail 24-hours-a-day, seven-days-a-week. Customers are asked to monitor updates on the Postal Service's website: www.usps.com, or by calling 1-866-545-USPS (8777). Press 1 for Manhattan information and 2 for national information. The Postal Service processes half of the world's mail volume by delivering 650 million pieces of mail daily, with 20 to 25 percent of that volume transported by commercial air. Following last Tuesday's FAA order to close America's air transportation network, the Postal Service utilized contingency plans to expand its ground transportation network. In addition to using its 210,000 postal vehicle fleet - the nation's largest - it also expanded use of the 6,000 to 7,000 trucking firms it contracts with daily. The number of vehicles owned by these firms can range from a few trucks to hundreds. The Postal Service also expanded the use of Amtrak rail transportation. Domestically, Express Mail, Priority Mail and First-Class mail began to fly through cargo air networks last Thursday. Cargo air carriers have also transported international mail.