WhatsApp E.164 Format Conversion Rules: Country Codes, Leading Zeros, and Special Encoding for Argentina and Mexico

WhatsApp requires phone numbers to follow the ITU-T E.164 international standard: starting with '+', followed by a 1-3 digit country code and the local number, with no spaces or symbols and a total length not exceeding 15 digits. Standard processing requires stripping local leading zeros and 00/011 exit prefixes, but Argentina (+54) needs a 9 after the country code with the mobile prefix 15 removed, and Mexico (+52) needs to retain or add a 1. This article provides the complete cleaning sequence from raw lists to standard E.164.