BT will cut costs for up to a million landline-only customers following a review by Ofcom.
According to the watchdog, telephone line rental prices have gone up, despite wholesale costs falling.
As a result, it has become increasingly concerned that landline-only customers have not been getting good value for money in recent years, compared with those who buy landlines bundled with other services, such as broadband.
BT has therefore responded by confirming that monthly bills for landline-only customers will be cut by £7 a month, which works out to a saving of £84 a year.
Almost 800,000 landline-only customers will not have do anything to claim the price cut, as it will appear on their bills automatically, while line rental and call costs will be capped at the price of inflation.
BT customers on its Home Phone Saver package will also be able to take advantage of the reduced rate, and will be given the option of staying on their existing package or moving to the standard product.
Ofcom has promised to step in if BT fails to honour its agreement, while it also hopes other providers will follow suit.
Jonathan Oxley, Competition Group Director at the watchdog, said: "For many people, their landline is their lifeline.
"But households who only have a landline - and no broadband - have seen their phone bills soar. Many are elderly, and have been with BT for decades."
Figures from Ofcom show that two-thirds of landline-only customers are aged 65 or over, while more than three-quarters have never switched provider.
"We’ve been clear that they must get a better deal," Mr Oxley continued.
"So I’m pleased BT has responded to our plans in full by cutting these customers’ bills."
BT has confirmed that the changes will come into effect from April 2018
In a statement, the company said: "We have listened to the concerns of our line-only customers and agreed to reduce the price of line rental for them by £7 a month, or £84 a year, which means they will only pay £11.99 a month for standard line rental."
BT added that it already offers low income customers on certain benefits a special tariff called BT Basic, while its Home Phone Saver option provides a "great value bundle for customers who want a traditional phone service, with Anytime calls and other benefits".