How do you make a phone call from US to Mexico?

You may be able to reach a North American (USA, Canada, etc.) toll-free number from Mexico by dialing it as if it were an ordinary geographic number in North America: dial 00 1 and then the ten-digit toll-free number; for example, 00 1 844 555 0123. In a few cases, the owner of a North American toll-free number may have special arrangements for the number to also be toll-free from Mexico, but in most cases you will pay international call charges. If the call does not go through, look on the web for an ordinary geographic number for the company you are trying to contact. The toll-free codes in North America are 800, 888, 877, 866, 855, and 844, with 833 and 822 reserved for future toll-free use.

Domestic toll-free numbers in Mexico use the prefix 01 800, and international toll-free numbers (Universal International Freephone Numbers, UIFN) use the prefix 00 800. Note that 00 1 800, 01 800, and 00 800 are three completely different codes.