You can find Internet access almost everywhere in Southeast Asia now. All hotels (from 3* standard) in tourist cities and towns are well equipped with Wifi Internet that is available to all guests free of charge.
Telephone: The telephone network is quite well developed in Vietnam as well as in other Indochinese countries. For domestic calls within a city or province, you do not need to dial the local codes
For external calls to other province or city, you must first dial the code of that province first, then the number (normally included in the number and add up about 10 digits)
For example from Vietnam to other countries: You first dial 00 then country code then number:
You press: 00 + 33 + number
To United State & Canada:
You press: 00 + 1 + number
To United Kingdom:
You press: 00 + 44+ number
From other countries to Vietnam: Dial 00 + 84 + city/province code (4 to Hanoi, Saigon 8, etc). And finally the number you want, normally of 7 or 8 digits (since 2008, the new number system is preceded with 3).
Mobile phones: Mobile phones operate well throughout Indochina, and outside to the world. No need to change the SIM card with roaming service but you might save by using local SIM card by either unlocking your phone or just buy a cheap one locally.
Post Office: There are post offices in all major cities. They are recognizable from a distance with blue logo of the operator. They can be found easily on map too.
Electricity: Electrical current is 220 volts and most hotels have plugs and adapters of both U.S and European standards.