Spanish telecom company Telefonica announced that the company has reached a final agreement to sell its U.K. mobile business unit O2 to Hong Kong's Hutchison Whampoa for GBP10.25 billion, which is about USD15.2 billion.

Telefonica and Hutchison Whampoa previously entered an exclusive negotiation on January 23, 2015, and the two parties reached a final agreement.

The transaction is expected to accelerate the integration of the British telecom industry. At present, Hutchison Whampoa is the owner of Three, a rival operator of O2, in the U.K. By acquiring O2, Britain's second largest mobile operator, Hutchison Whampoa will become the largest mobile operator in the country. O2 currently has about 22 million users.

Telefonica said that the transaction is still subject to the approvals of regulatory authorities and is expected to be closed before June 30, 2015. However, the company added that the final deadline may be postponed to September 30.