DC. The following year, the line's worth was proven in the Cuban Missile Crisis. With the possibility of a nuclear strike by the Soviet Union, the phone company hurriedly dispatched radio technicians to each site, often on a lonely mountaintop, to be ready to restore service in case of a failure. That route was upgraded to modern digital microwave technology in the early 1990s. Direct distance dialing (DDD) was first introduced in November 1972, just 21 years after its initial introduction in Englewood, New Jersey, and 14 years after introduction to Canada at Toronto and Montreal. It had become available on all but a handful of exchanges by the spring of 1980. The pole line remained used until the early 1980s for multiparty line service for rural telephone customers, who are now served by point-to-point radio connections for their telephone service. The removal of the wires provoked a small rural protest from people who had hooked their radio sets to the wire to pick up Canadian Broadcasting Corporation (CBC) radio signals, which inadvertently were carried along the wires. A Northwestel spokesperson explained in a letter to the editor that it could not knowingly continue to provide a service that it was not licensed to provide. The company's corporate headquarters were transferred from Edmonton to Whitehorse in 1980. Operations have been diversified, with Yellowknife being another prime centre for the company. (The years in which Hay River Tel. Co., Fort Smith Tel. Co., and Performance Communications were established is not known by the contributor of this chart.) Modern corporate history Northwestel was established in 1979 by its owner, Canadian National Railways, spinning off the "northwest" operations of Canadian National Telecommunications (which is not to be confused with CNCP Telecommunications, a joint venture that CP Telegraphs and CN Telegraphs formed). The Newfoundland operation was, the same year, spun off as Terra Nova Tel (TNT). TNT was later purchased by NewTel Enterprises and merged with Newfoundland Telephone in late 1988. Northwestel was sold to Bell Canada Enterprises (parent of Bell Canada) on December 1, 1988. Since then, Northwestel has become a direct subsidiary of Bell Canada, although still regulated by the Canadian Radio-television and Telecommunications Commission (CRTC) separately from Bell Canada, with its own method of regulation until 2007: rate of return. Northwestel, as of 2007, is regulated more closely like all other companies in Canada — price regulation and a split rate