On March 24, 2012, a fifth telephone area code, 667, will be added to join the existing Maryland codes of 301, 410, 240 and 443. Originally, 301 covered all of Maryland, but in 1991, the state was split in half and 410 was assigned to the other half. In 1997, codes 240 and 443 were added.
An excessive number of mobile devices and the multiple phone numbers assigned to them have forced the issue; we’re simply running out of numbers. Other states are adding area codes as well. According to an article in the Washington Post, the North American Number Plan is now issuing approximately 25 and 30 new area codes each year.