Area code 521 is for what city in Mexico?

Answer 1

There is no area code 521 in Mexico. However, when calling a mobile phone (cellphone) in Mexico from other countries, you must insert the prefix '1' in between the country code +52 and the geographic area code.

For example, a landline in Guadalajara begins with +52 33, but a mobile from Guadalajara begins with +52 1 33.

(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.)