Where is telephone country code 251 92?

Country code +251 (dialed as 00 251 from many places) is Ethiopia.

Mobile numbers begin with +251 91.

VSAT numbers begin with +251 98.

Landline numbers are divided into 8 area codes:

+251 11 = Addis Ababa (capital)

+251 22 = Nazret, southeast

+251 25 = Dire Dawa, east

+251 33 = Dese, northeast

+251 34 = Mekele, north

+251 46 = Awassa, south

+251 47 = Jimma, southwest

+251 57 = Nekemte, west

+251 58 = Bahir Dar, northwest

(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.)