Thailand's mobile market consolidated in 2023, when DTAC merged into TrueMove H to form True Corporation, leaving two major national networks: AIS and True Corporation (which continues to operate the True and legacy DTAC brands during the transition). Both offer solid coverage across Bangkok, the northern cities, the main beach resorts and the well-travelled tourist corridors; signal on smaller or more remote islands — a quiet bay off Koh Phangan, a less-developed stretch of Koh Chang, a mountain village in the far north — can be noticeably weaker than in Bangkok's BTS/MRT network or Phuket's main resort strip, so it is worth checking island-specific coverage before relying on a connection for anything time-critical off the beaten track.
Every local SIM in Thailand, tourist or otherwise, requires real-name registration under National Broadcasting and Telecommunications Commission (NBTC) rules: an original physical passport (no photocopies or phone photos accepted), plus, since mid-2025, a biometric facial scan matched against the passport. At an official AIS or True counter — available at Suvarnabhumi, Don Mueang, Phuket and Chiang Mai airports around the clock — staff complete this on the spot in roughly ten to thirty minutes. Buying from a 7-Eleven or convenience store shifts the registration step onto the buyer, who must complete it through the carrier's app, uploading a passport photo and a selfie, usually within a few hours of first use or the SIM is deactivated. An eSIM bought from an international provider before departure is a different product entirely: because it is a roaming connection issued by a foreign operator rather than a new Thai-registered line, Thailand's NBTC registration rule does not apply to it, and there is no passport scan or facial photo to submit at any point.
The practical sequence: install the eSIM profile over Wi-Fi before the flight, keep the home SIM active for calls, SMS and one-time passcodes, and switch on the data eSIM once landed, walking past the airport SIM counters rather than queuing at one.
