Customers who only buy landline services from BT are set to get at least £5 a month taken off their bills under plans set out by the telecoms regulator, Ofcom.
It said those customers, who are often elderly or vulnerable, were not getting value for money.
BT has nearly 80% of the UK landline market, and Ofcom is hoping other providers will also cut prices.
The telecoms giant said it took its responsibilities “very seriously”.
“Unlike other companies, [we] have many customers on special tariffs for socially excluded or vulnerable customers,” BT said.
“Recently, we have frozen the cost of line rental for all of our customers who take a BT phone line.”
The planned price cut will effectively reverse cost rises seen in recent years, Ofcom said. BT customers, who pay £18.99 per month for a landline-only contract, would pay no more than £13.99.