I don’t have exact numbers, but the Washington Post (you may find a paywall) has a series of maps that show how many people have ditched old-fashioned landlines and rely only on cell phones. The bluest states on the map have the fewest landlines. Idaho and Wyoming appear the bluest. States with the oldest-fashioned telephones are in the northeast. As a percentage, older Americans cling to the older system.
Research also shows that people who maintain a landline are doing better when it comes to income. They also have fewer troubles when it comes to the use of alcohol and tobacco! Maybe they can’t afford a drink if they’re paying for two phones.
Even with our dead zones when it comes to cellular coverage (and trust me, north of McCall I can never get service) the people of southern Idaho have especially adopted the new technology. Landlines are still common in the central highlands where the cell service is spotty. A county-by-county map shows the reliance on the technology.
I have a theory as to why the cell phone became the only means of communication for so many people in Idaho and Wyoming. People often do most of their work from behind a wheel. While ranching, farming, or driving a truck.
I gave up my landline a dozen years ago. I was pleased with my service, which was through FIOS, but why pay two bills every month when you can only talk on one phone at a time?