Two possibilities:
00 = commonly used international access prefix, not part of the country code
+1 = country code for North America (USA, Canada, etc.)
646 = area code for Manhattan, New York City, USA
001 = less common international access prefix
+64 = country code for New Zealand
6 = area code for New Plymouth and southern/eastern North Island
Because of the ambiguity caused by different international access prefixes around the world, it is best to quote an international telephone number without the access prefix, beginning with just the country code, prefixed only with a plus sign.
(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 +354 is Iceland.
Germany is country code +49.
Colombia is country code +57.
pakistan
The country calling code for Germany is 49. So 010 49 from the US.
Qatar is telephone country code +974.
Country code +357 is Cyprus.
No such code. +1 is the country code for America The calling code is therefore the three digits beginning with 60 in this case.
The International country calling code of Slovakia is +421.
The country code for Sweden is +46, no matter where you're calling from.
0021 is not the country code for England. England uses the United Kingdom country code +44 which is dialled as 00 44 from most of Europe or 011 44 from North America.
Ashburton, New Zealand is in the Canterbury Region, on the coast of the South Island. The country calling code for Ashburton is 302, 303, 307. 308, and 908. The country calling code is +64.