I was not able to get a prepaid SIM card in Siem Reap nor find any information about those in Cambodia. Our guide checked for us and told us that Cambodia didnt have prepaid. Does anyone know what company to use in Cambodia? Vietnam was no problem, there was a place selling SIM cards at very good prices at the Hanoi Airport. It is right in the arrivals area after you exit customs. Also, I would get the phone here and get the SIM cards there.