Mobile prepaid customers will no longer get an extension of time to register their SIM cards, in a drastic move to avoid the potential use of unregistered phone numbers to detonate bombs remotely.
The formal decision was made by the National Broadcasting and Telecommunications Commission (NBTC) in the aftermath of the Ratchaprasong bombing.
"Prepaid mobile users who failed to register their personal information by the July 31 deadline are now being cut off and are unable to use outbound mobile calling and data services," said NBTC secretary-general Takorn Tantasith.
Those users can still receive incoming calls and SMS messages for one more month.
"We can confirm that all existing unregistered prepaid numbers are in our control," Mr Takorn said.
A mobile phone without a registered SIM card cannot make a call or access the internet. Mr Takorn said this would prevent criminals using unregistered SIM cards from easily exploiting the numbers for illicit activity.
The cabinet approved the prepaid registration rule last month as part of the national security agenda.
Up to 67.8 million prepaid numbers, out of a total of 85.5 million issued numbers, have been registered with users' personal information.
Of the total 17.7 million unregistered numbers, 13 million are inactive users and the remaining 4.7 million are still active.
As of July 31, mobile leader Advanced Info Service (AIS) had 9.2 million unregistered numbers. Second-ranked Total Access Communication (DTAC) had 5.5 million unregistered numbers, while No.3 True Move had 3 million.
"We are in talks with the three major mobile operators on implementing measures to terminate all existing unregistered numbers within the next month," Mr Takorn said.
Operators must inform those users 30 days before cutting off their services, in line with regulations governing telecom service contracts.
Mr Takorn also said the NBTC's telecom committee on Wednesday approved changes in some key details of the planned 4G auction for the 1800-megahertz spectrum, scheduled to take place on Nov 11.
The changes came about in response to a public hearing on the auction.
According to Col Settapong Malisuwan, the NBTC vice-chairman, the reserve price for a 1800-MHz licence will increase to 15.91 billion baht, up from 13.92 billion previously.
The reserve price represents 80% of the estimated real spectrum value, up from 70%.
The duration of a licence term will be reduced to 18 years from 19 years, Col Settapong said.
In addition, the amount of bandwidth for a 1800-MHz licence will increase to 15 MHz, up from 12.5 MHz.
CAT Telecom has finally agreed to return its unused 5 MHz bandwidth on the 1800 MHz band to the regulator for this November's auction.