Returning visitors to Thailand faced frozen bank accounts and dead phone numbers after long absences, but simple low-cost steps could have prevented the disruption.
Mobile number loss stranded travellers at the airport
At Bangkok’s Suvarnabhumi Airport in November 2025, some part-time residents landed after months abroad and found their Thai phones showing only “no network” instead of the familiar AIS, True or dtac signals. Without mobile service, one-time passwords for Thai banking apps did not arrive, leaving accounts inaccessible until customers appeared in person at a branch with their passports. The scenario was described as a recurring problem affecting thousands of part-time expats and Thailand enthusiasts each year.
From communication tool to digital identity
In countries such as Germany, Austria or Switzerland, a mobile number typically served only as a communication channel, but in Thailand in 2025 and 2026 it functioned as a person’s digital identity. Almost all key services were linked to a single number, including PromptPay for cashless payments and the Line messaging app, as well as Lazada purchases and especially online banking. Losing that number meant losing the key to digital life in Thailand.
How prepaid validity quietly erased numbers
The report noted that Thai prepaid SIM cards effectively had two currencies: credit in baht and time-based validity. Customers could hold as much as 5,000 baht (around 135 euros) in credit, but once the validity period expired the SIM was first suspended and, after a grace period often as short as 45 days, permanently deleted. Remaining balances lapsed and the number returned to the provider’s pool to be reassigned.
AIS–True duopoly under NBTC rules
Since the merger of True and dtac into True Corporation—completed in 2023 and fully integrated operationally by 2025—the Thai mobile market had effectively become a duopoly alongside AIS. Even when “dtac” still appeared on handsets, customers were frequently using the same infrastructure as True subscribers, and the apps and service centres were increasingly merged. Rules on validity remained broadly similar across providers because they were regulated by the National Broadcasting and Telecommunications Commission (NBTC).
Regulation protected credit but not inactive SIMs
According to the account, NBTC regulations prevented prepaid balances from simply disappearing, but allowed operators to disconnect inactive numbers to save resources. Users therefore needed to simulate regular activity even while living abroad. Many tourists made what was described as a classic mistake by loading 500 or 1,000 baht at the airport, assuming that amount would last a year, although standard top-ups typically granted only around 30 days of extra validity per transaction.
Why high balances failed to keep lines open
Large unused balances often sat on SIM cards while the expiry date moved closer, with slow deductions from premium SMS subscriptions or accidental data roaming. The key objective was not “a lot of credit” but “a lot of time”, the report stressed, and time on Thai SIMs was bought through tactical use of low-value top-ups rather than large one-off payments. This distinction was identified as the main trap for long-term visitors.
The 12-top-up trick to buy a year of validity
A widely discussed tactic in expat forums, described as still effective in 2025, relied on the way AIS, True and dtac systems handled top-ups. Each individual recharge, no matter how small, extended SIM validity by 30 days. Minimum top-up amounts at Boonterm machines or via banking apps were often just 10 or 20 baht, enabling a sequence of low-cost recharges.
360 days for around 3.25 euros
Using an exchange rate of approximately 1 euro to 37 baht as of November 2025, a 10-baht top-up equated to about 0.27 euros. Twelve consecutive top-ups of 10 baht created 120 baht in credit, or roughly 3.25 euros, but were recorded as 12 separate transactions. Because each transaction added 30 days of validity, the SIM’s life was extended by 360 days, up to the statutory maximum of 365 days. The process could be completed within about five minutes.
Buying validity directly via USSD and “Mao Mao”
For users unwilling or unable to perform multiple transfers, Thai operators offered a second route: direct purchase of validity from existing credit using USSD codes. For dtac and True, there were options to buy an additional month of validity for around 2 to 3 baht, with a typical pattern allowing 90 or 180 days for about 15 baht deducted from the balance, depending on the code displayed in the app at the time. For AIS, so-called “Mao Mao” packages let customers purchase small bundles of minutes, such as 10 or 30 baht, that came with 30 days of extra validity.
Provider apps turned phones into remote controls
By 2025, using USSD codes from abroad could be unreliable when roaming networks faltered, so the safest approach was via operator apps such as myAIS, True iService and the dtac app. Travellers were advised to install these apps and log in before leaving Thailand, while they could still receive SMS verification codes. On the home screen, subscribers could see their main balance and, more importantly, the “valid until” date, and in the True and dtac apps often found dedicated menus labelled “Buy Validity” or “Extend Validity”.
Roaming needed for OTPs but data stayed off
To make remote management work and to ensure access in emergencies such as password resets, the SIM had to connect to a network abroad. Many expats reportedly switched off roaming completely for fear of high charges, a move later described as a mistake. Passive roaming—simply registering on a foreign partner network—was generally free, and receiving SMS messages, including one-time passwords, was typically free worldwide with Thai providers.
Managing roaming costs safely
Charges applied instead to receiving and making calls and to mobile data usage, which was described as particularly risky for costs. The recommended approach was to keep “data roaming” turned off at handset level while leaving the Thai SIM active. If a device did not automatically log into a partner network on arrival in Europe, it usually indicated that international roaming had not been enabled with the Thai operator, a step that needed to be completed in Thailand via code or in-store before departure.
Top-up hurdles without a Thai bank account
The 10-baht strategy worked best through mobile banking apps from Thai institutions such as Bangkok Bank, SCB or Kasikornbank. Tourists holding only accounts at European banks often faced higher minimum top-up amounts of 200 or 300 baht when using foreign credit cards in Thai provider apps, making repeated small recharges expensive and inefficient. To overcome this, they were advised to compare fees on third-party top-up websites or to ask Thai acquaintances for help.
Third-party platforms and local help
Websites like MobileTopup.com or Recharge.com were cited as options that sometimes supported smaller denominations, although the report urged users to examine fee structures carefully. Alternatively, travellers could ask Thai friends or hotel staff before departure to send multiple small top-ups—such as 12 transfers of 20 baht each—to their number in exchange for cash. For locals, such bank-app transfers reportedly took only seconds.
eSIMs seen as the future of Thai connectivity
Looking ahead to 2026, the account forecast the gradual disappearance of physical SIM cards in Thailand and recommended that holders of older plastic cards exchange them for eSIMs at AIS or True shops before flying out. Physical SIM contacts were prone to corrosion in humid air and could be lost, whereas an eSIM profile was stored digitally on the smartphone. In Europe, users could simply deactivate, but not delete, the eSIM profile to save battery and briefly reactivate it monthly to confirm network access and receive a test SMS.
Low-cost insurance against digital disruption
The report concluded that buying a new SIM on arrival at the airport for around 300 baht was possible, but the effort of updating banks, social contacts, apps and official records with a fresh number was far more onerous. A checklist for 2025 advised travellers to activate roaming, install the provider app, perform 12 consecutive small top-ups of 10 to 20 baht via a Thai banking app or through a friend, and then verify in the app that the “valid until” date lay roughly a year in the future.
Editorial note on changing conditions
For the equivalent of under four euros, visitors were able to secure their Thai digital identity for an additional year and arrive back in Bangkok with an immediately usable connection. An editorial note stressed that the information reflected the situation in November 2025, that exchange rates and operators’ USSD codes and conditions could change at short notice, and that travellers should always consult the latest app from AIS or True Corporation before leaving Thailand to confirm roaming status and SIM validity.