Laos is country code +856.
You must drop the trunk prefix '0' from the beginning of the Laotian number. For example, Vientiane's area code 021 becomes +856 21.
Mobile numbers begin with +856 20 (with 8 more digits). Landline numbers begin with +856 21 through +856 88.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
Louisiana is not a country, so it does not get its own telephone country code. The telephone country code for the United States (plus Canada and 18 assorted island countries and territories in or near the Caribbean) is +1.
The telephone area codes for Louisiana, as of 2014, are 225, 318, 337, 504, and 985.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
The country code and area code of Attapeu, Laos is 856, (0)36.
The country code and area code of Bokeo, Laos is 856, (0)84.
The country code and area code of Huaphanh, Laos is 856, (0)64.
The country code and area code of Loungprabang, Laos is 856, (0)71.
The country code and area code of Oudomsay, Laos is 856, (0)81.
The country code and area code of Pakse, Laos is 856, (0)31.
The country code and area code of Phongsaly, Laos is 856, (0)88.
The country code and area code of Savannakhet, Laos is 856, (0)41.
The country code and area code of Sayabouri, Laos is 856, (0)74.
The country code and area code of Xekong, Laos is 856, (0)38.
The country code and area code of Vientiane, Laos is 856, (0)21.
The country code and area code of Borikhamsay, Laos is 856, (0)54.