From Revolvy.com – Early beginnings of Northwestern Bell
It has never been definitively established where Northwestern Bell’s earliest roots lie. The earliest record of telephones in the Northwestern Bell service area was a two-telephone intercom circuit used by a Little Falls, Minnesota druggist and his clerk in 1876. A Bell-licensed exchange is believed to have opened in Deadwood, South Dakota between March and August 1878….
Full article at Revolvy.com – https://www.revolvy.com/topic/Northwestern%20Bell&item_type=topic