The northwestern part, stretching from the far west El Paso to the Texas Panhandle in the north and to Fort Worth in the east, was identified with area code 915.
The northeastern part of Texas, roughly from a line just west of Dallas to Waco, to the borders of Arkansas and Louisiana, had been assigned area code 214.
Available databases do not indicate the exact boundary lines, and it is probable that parts of 214 were included in the western suburban area of Dallas.
Due to the Metroplex's dramatic growth in the second half of the 20th century, the 817 was finally reduced in size in a three-way split on July 25, 1997.
This was intended as a long-term solution, but within two years 817 was once again nearing exhaustion due to the growth of telecommunication services in the Metroplex, particularly from the popularity of auxiliary, mobile devices.