The six were Advanced Wireless Network, the third-generation mobile arm of Advanced Info Service; Total Access Communication subsidiaries DTAC TriNet and DTAC Broadband; True Move subsidiaries True Move H Universal Communication and Hutchison Telecommunications (Thailand); and Jas Mobile Broadband, a subsidiary of Jasmine International.
The six companies also picked up bid documents late last month for the 1800-MHz spectrum auctions.
The 900-MHz auction documents are available until Oct 21, with the deadline for the submission of bids scheduled for Oct 22.
Takorn Tantasith, secretary-general of the National Broadcasting and Telecommunications Commission (NBTC), said he believed the auctions of two 4G licences each for the 1800- and 900-MHz spectra would intensify with a healthy competition.
The draft auction designs of the 900-MHz spectrum, which were published in the Royal Gazette last Friday, stipulate that the winners of the 900-MHz licences will have to roll out their 4G networks to cover half of the population within four years, increasing to 80% within eight years.
The NBTC initially planned to auction two licences on the 900-MHz spectrum on Dec 15, containing 10 MHz of bandwidth each.
The reserve price for a 900-MHz licence was set at 12.9 billion baht, or 80% of the estimated real spectrum value.
Mr Takorn, however, said the NBTC was considering rescheduling the auction date for the 900-MHz auctions earlier than the original plan, or holding both 1800- and 900-MHz auctions on the same day, Nov 11, in order to eliminate potential risks for those bidders who failed to win a licence on the 1800-MHz spectrum.
"We expect to finalise the auction date for the 900-MHz licences by Oct 15," he said.
On Monday, Deputy Prime Minister Wissanu Krea-ngam held talks with commissioners of the NBTC, ICT Minister Uttama Savanayana and the TOT president about the details of 900-MHz spectrum auctions.
Mr Wissanu disagrees with the NBTC's plan to auction the 1800- and 900-MHz on different days. He wants the regulator to hold both spectrum auctions on the same day in order to ensure fair play and avoid risks if the 900-MHz auction is delayed if the TOT files a lawsuit aimed at suspending the auctions.
Mr Takorn insists that NBTC will proceed with the planned 4G auctions as scheduled unless the court orders otherwise.