Phone calls can be made at public phone stations to use cards or to buy phone sims to call. A sim phone number buys about 2.5 USD equivalent to 150 Rup. At hotels, you can call Vietnam directly. The phone in the hotel is very expensive, so you should buy a phone sim - a type of international call to contact via mobile phone to Vietnam.
Call to Vietnam: 00 - 84 - VEHICLE + TABLE or MOBILE PHONE NUMBER (remove first 0).
Call from Vietnam to Russia: +7 495 + PHONE NUMBER (in Moscow) or +7 812 + PHONE NUMBER (in Saint Petersburg).
If your mobile phone is connected to the international network (roaming), when it comes to Russia, it will automatically detect the network.
You can completely use your phone when traveling to Russia. Phone waves are strong in large cities or towns but may be weaker in rural areas. And you should remember to register for Global Roaming before traveling to Russia.
Electricity used in Russia in the program is: 220V. Socket type is 2 round pins. Ideally, you should bring a "multi-purpose" intermediate outlet that you can use in any situation.