A mobile phone with a local SIM card (and an internet-based calls and messaging app) will allow you to get online and make phone calls in Vietnam.
Domestic calls are very inexpensive using a Vietnamese SIM.
Phone numbers in Hanoi, HCMC and Haiphong have eight digits. Elsewhere around the country phone numbers have seven digits. Telephone area codes are assigned according to the province.
It’s usually easiest to use wi-fi and a calling app such as Skype. Mobile phone rates for international phone calls can be less than US$0.10 a minute.
If you have an unlocked phone, it’s virtually essential to get a local SIM card for longer visits in Vietnam. 3G and 4G data packages are some of the cheapest in the world at around 150,000d for 3GB and will enable you to use the net if wi-fi is weak; some packages include call time, too. Many SIM card deals allow you to call abroad cheaply (from 2000d a minute).
Get the shop owner (or someone at your hotel) to set up your phone in English or your native language. The three main mobile-phone companies are Viettel, Vinaphone and Mobifone.
Most regional phone codes (59 of Vietnam's 63 provinces) changed in 2017. Inevitably, many publications and web pages have yet to update numbers using new codes.