Vodafone said it would finance the deal from existing resources and by issuing new shares, which it expects will raise £3bn.
The sale is "good value" for BT shareholders, with a return of more than three times its original investment in Japan, and five times in Spain, the company said in a statement. The proceeds of the sale will be used to reduce the carrier's £30bn debt burden, which has been increased by the cost of 3G (third-generation) mobile telecommunication licences.
BT said Japan Telecom and J-Phone are good companies and that the relationship has been "successful and profitable". BT believes both companies have a good future, but said Vodafone made an offer it could not refuse.
Vodafone will become the largest shareholder in Japan Telecom with a 45% interest, while its stake in mobile subsidiary J-Phone will grow to 46%, the company said. In Spain, Vodafone will own 91.6% of Airtel.
J-Phone is Japan's third-largest mobile operator with about 10 million customers; Airtel is second on the Spanish wireless market with more than 7 million customers, according to Vodafone.
Customers will not be affected from BT offloading its stakes, said BT spokesman David Orr.
"This financial deal has no impact on operations at all. It's good for BT and good for our shareholders. BT will still sell its (fixed line) services in Japan and the international relationship with Japan Telecom will stay the same. Roaming agreements in Spain will remain intact," said Orr.
Vodafone said that the increased stake in Japan Telecom offers it greater exposure to the development of 3G services in Japan and will allow it to enhance its wireless Internet knowledge. However, in Europe, the company's increased stake in Airtel, of which it already owned 73%, will not bring much change for the user, according to a company spokeswoman.
One analyst said Japan Telecom and J-Phone customers stand to gain most from the deal, with no detrimental effect on BT customers.
"The Japanese companies will no longer have to deal with a debt laden shareholder. With BT out of the way stability will return and the companies will be able to concentrate on services and customer demands," said Paolo Pescatore, a senior analyst with International Data Corp (IDC). He added that Vodafone customers will also benefit.
"Vodafone can export the (Japanese) knowledge and expertise to Europe for a European 3G network and later a worldwide service. The deal reiterates that Vodafone sees Japan as a very important strategic market," he said.
The Japanese part of the deal is expected to close in August this year, the Spanish part in June, said Vodafone.
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