Before you start

Original passport (physical, not a photocopy or photo — required by NBTC registration rules)
An unlocked phone (eSIM supported on AIS and True if your handset is eSIM-capable)
For postpaid only: a long-stay visa or work permit, and usually a Thai bank account for monthly autopay

Step-by-step

1
Decide prepaid vs postpaid
Prepaid is the default for nomads — no contract, no credit check, top up as you go, and you can switch carriers freely. A 'tourist SIM' (short 8-30 day unlimited-data plan, ~300-600 THB) is fine for arrival; for a longer stay just buy a standard prepaid SIM and add a monthly package. Postpaid (a billed monthly contract) is cheaper per-GB and better for heavy users, but requires a long-stay visa/work permit plus a Thai bank account or card for autopay, so most people only switch once settled.
In personWho: You5 minutes to decideFree (decision)
2
Buy and register a SIM (passport + face scan)
Buy at Chiang Mai airport arrivals, an AIS or True shop (in malls like Central Festival, Maya, Central Airport Plaza), or many 7-Elevens. Bring your physical passport — NBTC law requires passport registration, and since August 2025 a real-time biometric 'liveness' face check is mandatory for all new SIMs, so register at a staffed counter. eSIM is widely available on AIS and True — ask for a QR-code eSIM instead of a physical nano-SIM. Foreigners may hold up to three SIMs per operator.
In personWho: You (carrier shop staff register it)10-20 minutesTourist SIM ~300-500 THB incl. data; bare prepaid SIM ~50 THB
3
Add a data package and learn to top up
On a standard prepaid SIM, add a 30-day package: roughly 300-600 THB buys generous high-speed data (often marketed 'unlimited' with a fair-use cap, after which speed drops). Buy and manage packages in the carrier app — myAIS for AIS, TrueID for True — which also shows balance and expiry. Top up airtime anywhere: in-app by card, at any 7-Eleven counter, or via refill codes. Set the package to auto-renew if you don't want to think about it.
Mobile appWho: You5 minutes~300-600 THB / 30 days
4
Order home fibre (if not already included)
Check first — many Chiang Mai condos, apartments and co-living/co-working spaces bundle fibre into rent, in which case skip this. Otherwise order from AIS Fibre, AIS-3BB Fibre3 (3BB is now AIS-owned), True Online, or state operator NT. You'll need your address and passport/ID, and you book an installation appointment, typically within a few days to a week. A technician runs the line and sets up the WiFi router.
OnlineWho: You + provider technicianA few days to ~1 week for installation~500-800 THB/month for 300-1000 Mbps; install often free on a contract

Documents you’ll need

Original passport (mandatory for SIM registration)
Your face (live biometric scan taken at the shop, since Aug 2025)
Proof of address — e.g. rental contract or condo details (for home fibre install)
Long-stay visa / work permit + Thai bank account (postpaid contracts only)

Things most newcomers don’t know

It's now an AIS-vs-True duopoly — dtac no longer exists as a separate choice.

True and dtac merged in 2023 under True Corporation; the dtac brand is being wound down into TrueMove H. Treat the real choice as AIS (widest coverage, the safe default for Chiang Mai and its mountainous outskirts) vs True. NT, the small state operator, is cheap but a distant third on coverage.

Source: True Corporation / NBTC (2023 merger)

The August 2025 biometric face scan means you must register in person — pure-online foreign eSIMs got harder.

NBTC made real-time 'liveness detection' (a live face check) mandatory for every new SIM registration. A staffed AIS/True shop does this in seconds, but it's why you can't fully self-activate some plans remotely. Bring the actual passport — photos and copies are explicitly not accepted.

Source: NBTC SIM registration rules (effective Aug 2025)

Don't rush to buy fibre — check whether your place already includes it.

A large share of Chiang Mai's condos, serviced apartments and co-living/co-working spaces (Nimman especially) bundle fibre into the rent or have building-wide WiFi. Paying for your own line on top is a common newcomer waste. If you do install your own, you'll typically need the landlord's OK and an address on the account.

Source: Provider install requirements (AIS Fibre / True Online)

Common mistakes to avoid

Bringing a photocopy or phone photo of your passport — registration requires the original physical document
Assuming a 'tourist SIM' is fine long-term — it's capped at 60 days with no top-up extension; buy a standard prepaid SIM if you're staying
Reading 'unlimited' literally — most cheap packages are unlimited at full speed only up to a fair-use cap, then throttle
Trying to get postpaid on arrival — without a long-stay visa/work permit and a Thai bank account you'll usually be steered to prepaid
Forgetting to top up a bare prepaid SIM — let the airtime balance expire and the number can be deactivated

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.