When the North American Numbering Plan was established in 1947, Texas was divided into four numbering plan areas (NPAs), roughly outlining four quadrants in the state. Area code 713 was assigned to the southeastern part, from the Sabine River to the Brazos Valley.
On March 19, 1983, the numbering plan area was divided: the immediate Houston area retained 713, while the northern, eastern and western portions became area code 409.
On November 2, 1996, area code 713 was split again, with most of Houston's suburbs switching to 281. The dividing line roughly followed Beltway 8. Generally, most of Houston itself and most of the suburbs inside the beltway kept 713, while 281 served everything outside the beltway. But 713 was retained by all cellphone customers in the Houston area.
This was intended as a long-term solution, but rapid growth in demand for telephone services from the proliferation of pagers and cellphones required additional numbering resources within two years in both numbering plan areas. On January 16, 1999, the 713/281 boundary was removed, creating an overlay for the combined area, while simultaneously adding a third area code to the entire region, 832. As a result, ten-digit dialing became required for all calls in the Houston area.
On May 9, 2013, the Public Utility Commission of Texas (PUC) announced the addition of yet another code, 346, to the Houston overlay as of July 1, 2014.[1] This had the effect of allocating over 31 million telephone numbers to a service territory of eight million people. Exhaust projections of 2022 forecast that the Houston area will need a fifth area code by late 2025.[2] 621 has been reserved as additional overlay code; the PUC approved its implementation in 2023 to begin in January 2025.[3]
