Throughout much of the 20th century, there was just one provider of long-distance telephone services. AT&T operated a monopoly known as the Bell System. Compared to today, prices for phone calls were much higher. For example, the figure below lists the supply and demand curves for 5min weekday phone calls from New York City to Los Angeles per month in the 1980s (prices/costs are listed in today's dollars). The figure lists AT&T's Marginal Cost Curve, Isoprofit Curve A, Isoprofit Curve B, and Average Cost Curve. It also lists the Demand for these phone calls.

Long Distance Phone Calls in 1980 $10 $9 Marginal Cost Curve $8 $7 Isoprofit Curve A $6 Isoprofit Curve B Price $5 Average Cost Curve $4 $3 $2 $1.25 $1 Demand Curve O O 2 4 6 8 10 12 14 16 18 20 -22 24 Quantity (in hundreds of thousands of calls)