I am surprised that CMLink's SIM plans exclude Cambodia from its list of roaming destinations. It's the only glaring omission of all the SE Asian countries, if you exclude Laos and Myanmar too, which are shithole countries for other reasons so their exclusion is expected.
Tells you much about the development, or lack thereof, in Cambodia.
Reminder: Cambodia was so fucked up under Pol Pot, the Viet commies had to invade Cambodia to get rid of him.