Before 1996, 314 covered the entire eastern half of Missouri. In 1996, most of the old 314 territory outside of the St. Louis area became area code 573. This was intended as a long-term solution, but within two years 314 was almost out of numbers again due to the proliferation of cell phones, pagers and fax machines. The supply of numbers was further limited because the St. Louis LATA spills into much of southern Illinois, meaning several numbers that were part of area code 618 across the border in Illinois weren't available. As a result, most of St. Louis' outer-ring suburbs were switched to area code 636 on May 22, 1999. A permissive dialing period was allowed in which customers could still complete calls using 314.