52 (Five Two) is the International Country Code for calling Mexico.

00 (zero zero) is the International Dialing Code (Prefix) you use to make an overseas call from within the country of Mexico. 

Some calling cards purchased in the USA only have USA access numbers, so each time you call from Mexico you're paying long distance calling rates. But there are a few options.

Hotel Phones

Most hotels have a special pay phone that with cost you about $1.00 a minute but that is the only way you can call out without being charged an outrageous price.  The calling cards are located in the gift shops of your resort. Do not call long distance from your hotel room as many hotels contract out a second party long distance company which have inflated prices, some upwards of $7.00 USD a minute.

Calling Cards

Some calling cards work in Mexico, including a Costco MCI calling card, purchased in the USA. Just call the mci operator before leaving home to get the international access code to use in mexico.  It is only 36 cents using that card to call from mexico to the USA and 19 cents to call from the USA to Mexico.  Never ever use the pay phone at your hotel and by the way the MCI card is good all over the world. Just make sure your card has an access code for mexico.

Internet Cafes and Call Centers

You may also want to check with Cyber-Cafes and Coffee Shops for Internet Calling. Many places now offer VOIP calls and these are usually the best rates to the USA and Canada, anywhere from five to ten cents a minute. In most towns there are Long Distance call centers that offer low rates for international calls. 

Pay Phones

You will see regular LADA Tel or TelMex payphones in many public areas, along streets, in plazas. These do NOT take coins, but rather smart cards with a little gold chip that you can purchase in most kiosks, supermarkets, minisupers, etc. These offer regular TelMex rates, and possibly the best rates to the USA and other foreign countries, about 50 cents USD per minute.

Cell Phones

Many American cell phones will work in Mexico, depending on your location. Contact your phone company for instructions and rates. Rates for U.S. carriers in Mexico tend to be expensive. If your phone won't work where you're going or you would prefer cellular rates that are comparable to (sometimes better than) calling card rates, there are companies in the USA that will rent you a phone for Mexico. Both Cellular Abroad www.cellularabroad.com and Mexitel Cellular (www.mexitel.net) have programs that allow calls to be made from Mexico for $0.25 per minute and Mexitel has phones which provide international calls from specific cities in Mexico for $1 flat fee. Each company has phones which come with a USA phone number to which you can forward your calls from home and allow persons there to call without incurring international calling charges. Also, to save money on SMS to Mexico use a free SMS service such as SMS4all. 

You can also get a phone with a local Mexico phone number (eliminating roaming 100%), for about $ .06 cents per minute. www.roamfreemobile.com