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 area code for Warri, Nigeria, is +234 53. Within Nigeria, dial 053.
The country code and area code of Ilorin, Nigeria is 234, (0)31.
The country code and area code of Akure, Nigeria is 234, (0)34.
The country code and area code of Okitipupa, Nigeria is 234, (0)59.
The country code and area code of Uyo, Nigeria is 234, (0)85.
The country code and area code of Jalingo, Nigeria is 234, (0)79.
The country code and area code of Gusau, Nigeria is 234, (0)63.
The country code and area code of Lafia, Nigeria is 234, (0)47.
The country code and area code of Owo, Nigeria is 234, (0)51.
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.