Area code 443 is used for phone numbers in the United States. The area code covers a section of southern Maryland, including the cities of Towson, Dundalk and Baltimore.
During the 1940s, Bell Laboratories and AT&T co-invented the area code system used today. It was first implemented in 1947 and was being used across North America, including Canada, by the early 1960s. The original system used only 86 three-digit codes.
Rotary telephones were the standard at the time. The area codes that required the least amount of work on a rotary dial were given to cities with the largest populations. The rationale behind this method was to make the process easier for the largest possible number of callers. New York, Chicago, Los Angeles, Detroit and Philadelphia received the simplest-to-dial area codes. On the other end of the spectrum, low-population areas received area codes that would take longer to dial on a rotary telephone. These area codes were given to North Dakota, North Carolina, South Carolina and a section of Canada known as the Maritime Provinces.
There are 680 available area codes in the United States, of which 215 are in use as of 2014. Each area code has a maximum possible 10,000,000 phone numbers. Only 7,920,000 of those numbers are actually used to avoid numbers that start with 0, 1 or 911.