JOHANNESBURG, Aug 4 (Reuters) - South Africa's third-biggest telecom company Telkom said on Wednesday it has appointed the head of its consumer business, Serame Taukobong to be group Chief Executive Officer designate with effect from Oct. 1.

Taukobong, who is also a group Executive Committee Member, replaces Sipho Maseko who will step down at the end of June next year.

Taukobong joined Telkom in June 2018 and has extensive experience in telecommunications having spent about 10 years at rival MTN Group, where he held several senior roles which included Chief Operating Officer and later CEO of MTN Ghana, Telkom said.

As CEO of the Telkom Consumer Business, the mobile business customer base grew three-folds to 15 million and its revenue almost doubled to 20 billion rand ($1.40 billion) within a three year period, Telkom said.

Under his leadership, the mobile arm has become the third largest mobile business in South Africa, it said.

"The Board, Group CEO and the Group CEO Designate remain committed to structurally separate Telkom and unlock value for shareholders," the partly state-owned operator added.

Among the value unlock exercises, Telkom is looking for investors for its mast and tower business, which it reckons is undervalued since it is trapped in the group structure.

The exercise was started by Maseko who has been credited for successfully turning the operator around from a business facing declining fixed-line voice revenue, to a digitally-led one fit to compete with the top two players MTN and Vodacom Group

During this transition period, Taukobong will continue to have oversight of the Telkom Consumer Business, while a recruitment process for his successor starts immediately, Telkom said. ($1 = 14.2625 rand) (Reporting by Nqobile Dludla, Editing by Louise Heavens)