Telephone country codes never begin with zero.
Country code +857, which would be dialed as 00 857 from many places, is an unused code.
Country code +57, dialed as 008 57 from many places, is Colombia (South America).
To avoid confusion, it is best to write an international telephone number in correct international format, beginning with the plus symbol and the correct telephone country code (e.g., +850 or +57), omitting any dialing prefix.
(The plus signmeans "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.)
The telephone country code for Zimbabwe is +263. The area code for Glendale is 0376, or +263 376 in international format.
The telephone country code for Vietnam is +84. The area code for Bac Giang is 0240, or +84 240 in international format.
Leichtenstein is telephone country code +423.
where is telephone country code 1816
That is not a country code.
Fiji has telephone country code +679.
Country code +57 is Colombia.
Gibraltar is country code +350.
Moldova is country code +373.
Slovenia is country code +386.
Vanuatu is country code +678.
Niue is country code +683.