Where is area code 255?

There is no telephone area code +1 255 in North America (USA, Canada, etc.).

Country code +255 is Tanzania in East Africa.

There is no area code 255 in Mexico.

(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.)