Telephone country code +20 (dialed as 00 20or 011 20 from many places) is Egypt, and telephone area code +20 3 is Alexandria, Egypt.
There are also many places where a national number might begin with 203; for example, +1 203 is in Connecticut, USA, and +44 20 3 is a number in London, UK (country code +44, city code 20, local number beginning with 3).
(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.)
Country code +20 is Egypt, and a number beginning with +20 3 is a landline in Alexandria.
Leichtenstein is telephone country code +423.
where is telephone country code 1816
That is not a country code.
+20 is Egypt
The country code and area code of Duisburg, Germany is 49, (0)203.
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.