CenturyLink in CO does advertised a Basic $20/month plan on its website. See
CenturyLink | Home Phone for Clear Connection and Reliable Service.
Also, buried on the site is this, which is also buried on Verizon's.
"LifeLine Phone Service: Lifeline is available to residential customers only who qualify based on meeting income level eligibility requirements, and/or is receiving benefits from a qualifying federal assistance program, and requires remaining eligible for the entire offer period. The Lifeline program is a governmental assistance program that provides discounts on telephone service to qualifying consumers in every U.S. state, territory, and commonwealth. The amount of discount and qualifications for participation can vary by state. Consumers may be eligible if they participate in certain federal or state assistance programs or have a household annual gross income at or below 135% of the federal poverty level. Qualifying residents of American Indian and Alaskan Native tribal lands may also be eligible for up to an additional $25 per month of enhanced Lifeline support. Additionally, a discount on the one-time charge for establishing service may be available for qualifying residents of tribal lands through the Tribal Link-Up program. The Lifeline discount is available for one telephone per household, which can be either a wireline or wireless telephone. Lifeline service is not transferable, and only eligible consumers may enroll in the program. Documentation of eligibility is required to enroll. Consumers who willfully make false statements in order to obtain Lifeline telephone service can be punished by fine or imprisonment and can be barred from the program."
IIRC, this program is funded by the USF fee/tax on most everyone's phone bill. And is required of any of the old-school wireline ex-Bell companies, as they are public utilities.
But like
jiminnm said above, you have to know to ask for (aka insist on) these plans.