Bharti Airtel Ltd., India's largest mobile-phone operator, will spend $1 billion to expand transmission towers before joining rival Reliance Communications Ltd. in selling shares in the unit to investors. Bharti Airtel plans to sell a stake in the wholly owned tower subsidiary, Chief Executive Officer Manoj Kohli said in an interview today, without giving a timeframe. The unit will grow to be the world's biggest by the end of the year, he said. “A separate tower company gets a much better valuation than a single entity,'' said Mahesh Patil, who helps manage the equivalent of $1.5 billion in equity assets at Birla Sun Life Asset Management Co. in Mumbai. The incremental value creation in Bharti's case could be as much as $12 billion, said Patil, who has Bharti as his largest holding. Reliance Communications, India's second-largest wireless operator, valued its tower assets at 270 billion rupees ($6.7 billion) when it sold a 5 percent stake, more than the entire company's market value when it went public last year. […]