Port Harcourt, Nigeria, is in area code 084, which becomes +234 84 from outside Nigeria.
(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, and many other countries use different prefixes.)
The country code and area code of Aba, Nigeria is 234, (0)82.
The country code and area code of Abakaliki, Nigeria is 234, (0)43.
The country code and area code of Abeokuta, Nigeria is 234, (0)39.
The country code and area code of Agbor, Nigeria is 234, (0)55.
The country code and area code of Ahoada, Nigeria is 234, (0)86.
The country code and area code of Akure, Nigeria is 234, (0)34.
The country code and area code of Asaba, Nigeria is 234, (0)56.
The country code and area code of Awka, Nigeria is 234, (0)48.
The country code and area code of Azare, Nigeria is 234, (0)71.
The country code and area code of Bauchi, Nigeria is 234, (0)77.
The country code and area code of Enugu, Nigeria is 234, (0)42.
The country code and area code of Gombe, Nigeria is 234, (0)72.