You can buy a cheap cell phone with service for about $15 US or less at any phone store. Claro sells them for about 500 pesos. Comes activated with 100 pesos in it. You can just add minutes when you need it with a phone card or the machines that you put money in and your number, so it goes directly to your phone.
Also all incoming calls will be free, and all calls to the US are charged the same as local calls.
