There is no telephone area code 21 in North America (USA, Canada, etc.), but there are several area codes in the range 210 through 219.
Other countries may have an area code 21 or similar.
There is no telephone country code +21.
+211 = South Sudan
+212 = Morocco
+213 = Algeria
+216 = Tunisia
+218 = Libya
(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.)
The area code for Karachi, Pakistan, including Nazimabad, is +92 21. Within Pakistan, dial 021.
The country code and area code of Tkrit, Iraq is 964, 21.
The country code and area code of Parwan, Afghanistan is 93, (0)21.
The country code and area code of GuantÌÁnamo, Cuba is 53, (0)21.
The country code and area code of Vientiane, Laos is 856, (0)21.
The country code and area code of Morang, Nepal is 977, (0)21.
The country code and area code of Asuncion, Paraguay is 595, (0)21.
The country code and area code of Lausanne, Switzerland is 41, (0)21.
The country code and area code of Same, Timor-Leste is 670, 21.
The country code and area code of Lisboa, Portugal is 351, 21.
The country code and area code of Shanghai- SH, China is 86, (0)21.
The country code and area code of Novi Sad, Serbia is 381, (0)21.