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".
Speculation last month had pegged American Tower as the most likely buyer for the sites.
Service revenue declined as a result of intense price competition from the new entrant and aggressive incumbent responses, Vodafone said.
Yesterday's announcement was made alongside Idea announcing a fourth consecutive quarterly loss.
The statement said that after Vodafone India and Idea have completed their merger, around 6,300 co-located tenancies of the two operators on the combined standalone tower businesses will coalesce into single tenancies over a period of two years without the payment of exit penalties.
Consistent returns in the longer term have also attracted private equity investors to the market, although in the near term mast operators will struggle to grow revenue as some of their tenant phone network operators merge or shut down. The company also added 10 million broadband users YoY to close at 46 million 3G/4G subscribers.
Vodafone India and Idea Cellular on Monday said they have agreed to sell the roughly 20,000 towers that they directly own to a local arm of American Tower Corp. for $1.2 billion (Rs 7,850 crore) cash, a move which will help the two merging telcos pare debt while boosting the tower portfolio of the U.S. company in a market seeing massive 4G rollouts.
The telco's average revenue per user stood at Rs 132 in the second quarter compared to Rs 141 in the first quarter of the financial year.
Bank of America Merrill Lynch advised Idea on the American Tower deal, while Morgan Stanley advised Vodafone India.
Shares in Idea closed 3.8 percent lower at 93.35 rupees, while the Mumbai market index was down 0.94 percent.