Below are the clave lada for more than 200 Mexican cities.
Phone numbers are 7 digits everywhere except those cities, where the phone number has 8 digits.
The Cellular Abroad phone company can rent you a cell phone for Mexico and the world, sell you a SIM card if you have an unlocked phone, or sell you an unlocked phone. Check them out (opens in a new window, so you can browse area codes at the same time).
BTW, you MAY get a discount if you use "Mexicomike" in your online order or if you call them at 800-287-5072. To dial a Mexican cell phone from outside Mexico, add a "1" before the number and after the 011-52 (the prefix for dialing Mexico from the USA).
My searchable Mexican city area code locator will let you search for more than 250 Mexican area codes (lada) by Mexican city, Mexican state or area code number.