The move comes after a 12-year-old boy ran up a 200,000-baht bill playing Line's Cookie Run game on his mother's phone.
Takorn Tantasith, secretary-general of the National Broadcasting and Telecommunications Commission (NBTC), said the five mobile operators had agreed to improve their billing systems and impose a data-use limit of 1,000 baht for phones.
Even so, the regulator wants to set out proper regulations and establish reliable service standards.
Mr Takorn said the NBTC hopes to eliminate loopholes in mobile game downloads involving the purchase of content as well as game items and stickers.
The NBTC's legal panel next week will start looking at the details of bill payments to mobile operators, he said.
The regulator yesterday held a meeting with mobile operators and representatives of Google Thailand to discuss the planned regulations.
"The mobile operators agreed yesterday to set up a credit limit on the purchase of game items and alert smartphone owners when they are close to reaching their usage limits," said Mr Takorn, adding that operators must send customers a message every time they complete a download.
"We plan to discuss possible technical issues again at the next meeting on Wednesday."
Advanced Wireless Network (AWN), the 3G arm of Advanced Info Service (AIS), currently gives its Android-based phone users the ability to pay for various services and Google Play content through direct carrier billing (DCB).
The payment service began on April 30, letting AIS customers pay for content and services via their monthly billing system without having to use a credit card.
But AWN suspended the service on May 30 after complaints over bill shock.
Second-ranked operator Total Access Communication (DTAC) and third-ranked True Move are also negotiating with Google to provide such payment services.
NBTC member Prawit Leesathapornwongsa said AWN plans to resume its downloading service on the DCB platform by mid-July.
Unlike AIS, he said, DTAC and True Move have proposed providing payment services for mobile app downloads under a single billing system, meaning the companies would include all of a customer's monthly mobile services in a single bill.
Mr Prawit said the NBTC would probe the details of AWN's billing systems and the smaller rivals' single platform.
AWN told regulators its DCB system should not fall under telecom regulations since the company only acts as a payment agency for Google Play, unlike the single billing system of DTAC and True Move, he said.
AWN has 13,700 customers in its DCB system.
The NBTC also wants Google to ask customers to enter a PIN code for each download, Mr Prawit said.