The tower business will be sold at an enterprise value of 40 billion rupees ($613 million) to ATC Telecom Infrastructure Pvt Ltd, a unit of American Tower Corp, Idea Cellular said in a statement.
Both the telecom companies are in the process of merging their operations, which is expected to be completed next year and will displace Bharti Airtel as country's largest telecom operator.
The infrastructure investment firm is paying a combined INR78.5 billion ($1.2 billion) for the 20,000 tower sites owned by the two towercos.
Idea and Vodafone's Indian unit are now merging in a move that will see them overtake Airtel as India's largest telecoms operator with more than 400 million subscribers.
In the event that the completion of the sale of the standalone tower businesses precedes the completion of the proposed merger of Vodafone India and Idea, Vodafone India will receive Rs 3,850 crore ($592 million) and Idea will receive Rs 4,000 crore ($615 million).
American Tower CEO Jim Taiclet said: "We expect the addition of these two high quality portfolios to be highly complementary to our existing assets and to contribute to long-term leasing growth as India's leading mobile operators accelerate their 4G network deployments". This transaction follows the announcement in March by Vodafone India and Idea to sell their standalone tower businesses to strengthen the balance sheet of the combined business. The American company had earlier acquired a controlling stake in Viom Networks.
The numbers have come in the backdrop of pressure easing out on the industry after Reliance Jio started charging customers in April; it has increased tariffs thrice since then, after offering services for free for nearly six months.
Idea Cellular has posted a consolidated net loss of Rs 1,106.80 crore for the second quarter (July-September) of 2017-18 fiscal.
An global arbitration tribunal in February next year will begin trial on Vodafone's challenge to India using a retrospective legislation to seek Rs 22,100 crore in taxes, the British firm said on Tuesday.