Idea Cellular shares gained as much as 5.5 per cent to Rs 111.75, posting their biggest intraday percentage gain in over two weeks.
Vodafone Group and Idea are likely to seal a merger pact within a month, according to a media report.
Vodafone had confirmed on January 30 it was in talks to merge its Indian unit with local rival Idea in a deal that would create a new market leader better able to contest a brutal new price war.
Idea Cellular shares have risen about 35 per cent since January 27, when the companies confirmed talks of a merger.
Idea and Vodafone India did not immediately respond to email queries from Reuters.