force the wireless phone companies to reduce monthly charges for customers who have paid their phone subsidies.

Phone companies charge subsidies to offset the cost of new phones. Customers pay those subsidies over the period of the contract. If you terminate the contract early, you are charged a large Early Termination Fee (ETF).

When a customer has completely paid off the subsidies, their phone bill should be reduced to reflect that they "don't owe the phone company for the phone" anymore.