The firm has agreed to sell its 21% share of SmarTone, Hong Kong's third biggest mobile operator, to property developer Sun Hung Kai Properties for about HK$1bn (£84m; $132m).
The sale price is about a third of the sum that BT paid for its stake in the Hong Kong firm three years ago.
The deal is the latest in a round of overseas asset disposals launched two years ago by BT in an effort to pay off its debts, which at the time approached £30bn.
Debt pressure
"The transaction, which is expected to complete in January, is part of BT's disposal of non-core assets and another step in its debt reduction programme," the company said in a statement.
BT built up its crippling debt burden during a late-1990s acquisition spree, and by buying licenses needed to operate third generation mobile services in government-run auctions.
While BT's subsequent decision to retrench was seen as an embarrassing reversal of its lofty global ambitions, the asset disposal strategy had reduced its debt to just £13.1bn by late September this year, earning plaudits from investors.
The SmarTone sale reduces BT's Asian interests to a 16.6% stake in South Korean mobile firm LG Telecom, and an 11.9% share of Singaporean telecoms firm StarHub.
Profits boost
It follows BT's disposal of its one third stake in Malaysian mobile giant Maxis Communications last year.
SmarTone made a profit of about £13m in the year to late June, its first in three years.
The BT deal will make Sun Hung Kai SmarTone's majority shareholder.
The transaction could help boost Sun Hung Kai's earnings, helping to offset the impact of a sharp slump in Hong Kong property prices.
~RS~a~RS~International~RS~q~RS~~RS~z~RS~17~RS~)