 In 1951, 816 was reduced to Kansas City and the northwest, while southwest Missouri was assigned 417.Even with the presence of Springfield, the state's third-largest city, it is one of the most thinly populated area codes in the nation.Despite the growing proliferation of cell phones and smart phones (particularly in and around Springfield), 417 is nowhere near exhaustion; under current projections, the region will not need another area code until 2031 at the earliest.