Telephone country code +234 is Nigeria. A number beginning with +234 81 is a mobile from 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, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
234 is the international country code for Nigeria - however - I can't find any reference to an area code starting 81 !
The phone number 234 is the country code for Nigeria. The specific area code 81 is used for mobile phones in Nigeria. Therefore, the phone number 234 81 xx xx xx xx is likely from Nigeria, specifically a mobile phone within the 81 area code.
The country code and area code of Akumi District- Yamagata, Japan is 81, (0)234.
The country code and area code of Aichi, Japan is 81, (0)52.
The country code and area code of Daito- Osaka, Japan is 81, (0)72.
The country code and area code of Gifu, Japan is 81, (0)58.
The country code and area code of Fujisawa- Kanagawa, Japan is 81, (0)466.
The country code and area code of Abashiri District- Hokkaido, Japan is 81, (0)152.
The country code and area code of Atami- Shizuoka, Japan is 81, (0)557.
The country code and area code of Hitachi- Ibaraki, Japan is 81, (0)294.
Nigeria is +234. Numbers beginning with +234 80 or 81 are mobiles, with 8 more digits. Numbers beginning with +234 82 to 89 are landlines, with 5 or 6 more digits. For example: +234 80 xx xx xx xx = mobile +234 88 xxxxx or +234 88 xxxxxx = landline in Umuahia
The country code and area code of Mie, Japan is 81, (0)593.