Sim cards are cheap and worth the trouble. You can pick them up at many ports of entry, and the Phnom Penh airport even gives SIM cards for free with unlimited prepaid plans (which are usually a bit pricier than the local plans, but hassle-free.)
We recommend Smart or Cellcard– these are the biggest and fastest operators in Cambodia. Smart and Cellcard shops at the airport will charge around $7 for a sim card with unlimited data for a fixed time. If you’re going to get one later, make sure you bring your passport as all SIM card purchases usually need to be registered.
Alternatively, many street-side cellphone shops also sell sim cards. You’ll find them around any market- just look for the stores displaying cellphones in the glass cases. They will charge about $3 but passports are not required. English will be limited, and the sim card will have no balance, but by using a pre-paid plan you could spend less than $5 a month on plenty of data, texts, and local calls.
Data here is very cheap, and $2 for a week-long stay is more than enough pre-paid phone credit to buy. It’s easy to purchase additional credit any time by visiting a street-side mom-and-pop shop (the ones that sell a little bit of everything, with a big orange cooler out front). If you’re not sure, literally ask anybody to point you in the right direction and you will get help. Let the vendor know what carrier you’re using and how much you’d like to top-up. They’ll give you a scratch-off code card that has instructions on how to input on your phone.
If you are visiting the islands off the southern coast: please check if your hotel has wifi. The islands have to set up their power and water independently, but they can’t set up cell towers, etc, so many hotels do not offer wifi there. Those that do often have very shaky connections (check the reviews, people!)
Metfone is also a good choice as it is more reliable on the islands, but it’s not as commonly used on the mainland and will be harder to top-up. The islands are perfect to escape the modern world, but if you need to be contactable or if you are staying for a long time it could be worth just getting another Metfone sim for that leg of the trip- or re-booking someplace that has reliable wifi.