Before you start

Your original passport for registration
An unlocked phone
A sense of how far out of town you will actually go

Step-by-step

1
Choose Metfone if you leave town regularly
Metfone (Viettel) has the deepest provincial coverage, which matters on the roads out to the outlying temples, the Tonlé Sap floating villages and the airport corridor. Smart and Cellcard are perfectly good in town and often cheaper on data bundles.
OnlineWho: YouMinutesFree to choose
2
Register the SIM to yourself at an official store
Use an official carrier shop or the airport counter, not a market kiosk. Staff scan your passport and register the number to you. A SIM registered to somebody else cannot be recovered and will eventually break your bank app's two-factor authentication.
In personWho: You~15 minSIM from about USD 1–2
3
Add a monthly data bundle
Plain prepaid credit burns fast. Buy a data package in the carrier app or at any phone shop — a few dollars gets a generous monthly allowance, and Cambodian mobile data is among the cheapest in the region.
Mobile appWho: You~5 min~USD 3–10/month
4
Get home fibre, and ask about the building first
Fibre from Online, SINET or EZECOM reaches most of central Siem Reap and is cheap. Coverage thins as you move away from the centre, and installation in an older guesthouse-style building can take weeks. Ask what is already installed before you sign a lease.
In personWho: You (with your landlord)Days to weeks~USD 15–30/month
5
Keep a second network for outages
Power cuts and fibre faults are more common here than in Phnom Penh, particularly in the wet season. A cheap second SIM on a different network, with a data bundle, converts an outage from a lost day into an annoyance — which is why most remote workers in town run one.
In personWho: YouOne extra shop visitA few dollars a month

Documents you’ll need

Original passport (mandatory for registration)
Your phone, unlocked
Local address for home fibre
Cash or card

Things most newcomers don’t know

Coverage is a town-versus-province question here, and Metfone wins outside the ring road.

In central Siem Reap all three networks work fine. The difference shows on the roads to Banteay Srei, Beng Mealea and the Tonlé Sap villages, and along the fifty-kilometre corridor to the new airport, where Metfone's Viettel-built rural network is noticeably more reliable. If your work or your weekends take you out of town, that is the deciding factor.

Source: carrier coverage maps; community-reported

TRC rules require every SIM to be tied to an identified holder, and Cambodian banking is entirely OTP-driven. A number registered to a shop or a friend cannot be recovered if the phone is lost or the SIM is deactivated, and unpicking it later means producing the original registrant. Fifteen minutes at an official store on day one avoids all of it.

Source: Telecommunication Regulator of Cambodia; carrier registration terms

Two networks is standard practice among remote workers here, not paranoia.

Siem Reap's power supply and fixed-line infrastructure are less robust than the capital's, and the wet season brings both outages and faults. Because a second SIM with a data bundle costs a few dollars a month, the cost-benefit is trivially in favour of redundancy — which is why almost everyone working online in this town carries one.

Source: community-reported

Ask about fibre before the lease, because retrofitting is slow away from the centre.

Central Wat Bo and Kandal Village are well served; buildings further out, and the converted guesthouse stock that makes up a lot of the rental market, may not be. Installation needs the owner's consent and can take weeks. A flat with a live fibre drop is materially more valuable than one without, and it costs nothing to ask at the viewing.

Source: community-reported

Common mistakes to avoid

Buying a SIM registered to the shop and losing bank OTP access with the phone
Choosing a network on in-town coverage when your work takes you out to the temples
Running on raw prepaid credit instead of a data bundle
Signing a lease on a building with no fibre and no realistic way to get it
Having only one network in a town where outages are routine

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