The new rule will apply to 3G operators for both voice and data tariff rates, said Settapong Malisuwan, chairman of the NBTC's telecom committee.
The broadcasting and telecom regulator has come under pressure to ensure consumers will not lose out to operators who have been awarded licences to provide 3G services at prices many academics and activists deem as too low.
On Tuesday, the NBTC auctioned off nine, 15-year licences for 41.6 billion baht, only 1.125 billion baht or 2.78% above the reserve price.
The country's three main operators - Advanced Info Service (AIS), Total Access Communication (Dtac) and True - paid about the same in concession fees to provide 2G services for one year.
According to Col Settapong, the NBTC set a maximum rate of 99 satang per minute for existing 2G mobile services.
"It is expected that the new 3G price ceiling will be introduced before commercial 3G services are launched," Col Settapong said.
He added that the NBTC is authorised to draft the price regulation after the winning operators acknowledge their 3G overhead costs including the auction prices and network construction.
"We're trying our best to get all benefits through to consumers and members of the public," Col Settapong said.
NBTC secretary-general Thakorn Tantasit said operators must submit their price ceilings for 3G services to the regulator for approval before they can start charging customers.
The three licence winners have planned to invest a combined 110 billion baht in 3G network construction over the next three years - 50 billion from AIS, 40 billion from Dtac and 20 billion from True.
The NBTC chief yesterday also said the 3G bid was held lawfully under the Frequency Allocation Act. The law allowed it to determine the bidding method, structure and conditions, he said.
Mr Thakorn was responding to a petition filed by Supa Piyajitti, deputy finance permanent secretary and chair of the e-auction committee, to both the NBTC and the National Anti-Corruption Commission.
Ms Supa claimed the NBTC's Tuesday auction violated the government's e-auction rules, failed to generate real competition and may have contravened the 1999 State Bidding Act.
Mr Thakorn argued that the NBTC is an independent entity set up by the constitution. It is not under the Finance Ministry and not subject to e-auction rules applicable to government agencies.
Ms Supa's allegations were not valid, he said.
The NBTC yesterday also wrote to finance permanent secretary Areepong Bhoocha-oom to take his deputy Ms Supa to task.
The NBTC said Ms Supa's petition and her interviews with the media have misled the public into believing that the NBTC broke the law.
Santichai Santawanpas, deputy director-general of the Commerce Ministry's Internal Trade Department, said since the 3G auction was held legally, evidence must be found to prove there was price collusion among bidders.
As for the trade competition law, he said it is used to settle business-to-business complaints. For the 3G bid, the Commerce Ministry will not get involved unless a company files a complaint with it.
Despite the ongoing challenges, the NBTC yesterday formally declared the three bidders as auction winners.
Executives of the three winners, Advanced Wireless Network, Dtac Network and Real Future - subsidiaries of AIS, Dtac and True respectively - picked up their certificates yesterday. AIS also paid half of its bid - 7.8 billion baht - to the NBTC.
The NBTC secretary-general said the commission would grant the 3G licences to the three bidders within seven days after their up-front fees are paid.
Meanwhile, the Administrative Court yesterday rejected a petition filed by Boonchai Rungruengpisalsuk, head of the Telecommunication for People campaign group, over the NBTC's failure to set an auction ceiling price.
The court ruled that the NBTC has so far not violated Mr Boonchai's rights. This could change if the operators overcharge customers and the NBTC ignores calls to intervene, it said.
A source said the court had also given rulings on petitions filed by two other plaintiffs - Pongthiti Pongsilamanee and Narapol Plainet. The rulings are currently being sent to the plaintiffs.
Only the petition filed by Green Politics group leader Suriyasai Katasila is awaiting a ruling.
The Information and Communication Technology (ICT) Ministry meanwhile threw its full support behind the 3G auction outcome, saying the authorities should now move on to prevent further losses for the country.
Previous delays in 3G licensing have already caused damages of up to 100 billion baht in the past two years, said Chaiyan Peungkiatpairote, the newly appointed ICT permanent secretary.
The ICT Ministry plans to ask the NBTC to reallocate existing available frequencies for 4G technology.
Mr Chaiyan however said two urgent issues must be resolved. First, the recall of the 900Mhz frequency from TOT Plc and the 1800Mhz frequency from CAT Telecom after the existing concessions expire.
Second, the authorities must choose appropriate frequencies for 4G technology to provide high-speed broadband infrastructure nationwide under the government's smart network project.