Where is telephone area code 0440375?

There is no country code +0375, because telephone country codes never begin with zero.

Country code +375, dialed as 00 375 from many places, is Belarus.

(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.)