BT says it will pay �2bn into its pension fund to help cover the scheme's deficit.
It is one of the biggest one-off payments yet made by a company into a pension fund.
The payment is part of a nine year plan to bolster the scheme, which at the last valuation in June had a deficit of �4.1bn.
Supporting the pension fund has dragged down BT's performance. Back in 2008, the fund had a deficit of �9bn.
Under the latest plan, BT will make nine further annual payments of �325m.
BT's pension fund has 330,000 members, making it one of the biggest private sector schemes in the country.
"This agreement, under which the company makes an immediate contribution to the scheme of almost half of the deficit, reflects BT's financial strength and re-affirms our commitment to the scheme," said chief executive Ian Livingston.
BT, Royal Mail and Trinity Mirror - there is quite a lot going on in the fraught world of final salary pensions. �
"BT's long-term sustainable cash generation has improved significantly since the 2008 valuation and we remain focussed on improving BT's financial strength, investing in our future and enhancing shareholder returns."