The current format
Calling Mexico from a US landline: dial 011, then 52, then the 10-digit number. From a mobile phone or most VoIP services, you can substitute a "+" for the 011 -- so +52 followed by the 10 digits works the same way.
| Step | What to dial |
|---|---|
| 1. Exit code (landline) | 011 |
| 1. Exit code (mobile/VoIP) | + |
| 2. Country code | 52 |
| 3. Local number | 10 digits, area code included |
Mexico's 2019 reform: no more extra digit for mobile numbers
Before August 2019, calling a Mexican mobile number required inserting an extra "1" after the 52 country code, and domestic Mexican calls used separate 01, 044, and 045 prefixes depending on whether the call was long-distance or to a cell phone. Mexico's telecom regulator eliminated all of that in the 2019 reform: every Mexican number, landline or mobile, is now dialed the same simple way, with no extra digit and no prefix distinction. Plenty of "how to call Mexico" guides published before 2019 are still online and still describe the retired format -- if a source tells you to dial an extra 1 for a Mexican cell phone, it's out of date.
A worked example
A Mexico City landline formatted as 55-1234-5678 becomes 011 52 55 1234 5678 when dialed from a US landline, or +52 55 1234 5678 from a mobile.