Companies have to submit their bids by Aug. 30, Natee Sukonrat, a member of the National Telecommunications Commission (NTC), told Reuters in a text message. "We don't know how many rounds the auction should take. That depends on the number of interested bidders," he said. The process could be disrupted if parties opposed to the procedures seek a court order to put it on hold, Natee said. The upcoming auction has attracted interest from leading Asian telecoms firms during recent roadshows, the regulator said on Thursday.

The enhanced service will enable operators to tap new revenue through music, video, picture and data services, in a country of 67 million people where almost everyone has a mobile phone. The NTC has in fact decided to go beyond 3G and auction licences in September for a more advanced 3.9G service based on the same 2.1 GHz spectrum.

The auction for three licences with a starting price of 12.8 billion baht ($397 million) would generate at least $1.2 billion for the state. The licensing of 3G is a crucial step in the reform of the $4.7 billion sector because it will involve changes in the way companies pay fees to the government, analysts say.

The top three mobile phone operators are keen to receive 3G licences, which analysts say should reduce their regulatory costs. Shares in Thai telecoms firms outperformed the market on Friday as investors saw an increased chance of the 3G auction happening after the bidding rules appeared in the Royal Gazette.

At 0500 GMT, shares in second-largest mobile operator Total Access Communication were up 2.8 percent, while True Corp had gained 1.8 percent. True Corp controls unlisted True Move, Thailand's third-largest mobile operator. Market leader Advanced Info Service was up 0.54 percent, while the broader marker was just 0.01 percent higher.