Dont have any info for paticular companies, but I imagine your best rate would be to purchase a local sim in each country you are in. If you are a AT&T customer, for instance, rates will run from $.99/min in Mexico to $3.49/min in Belize, with the other central American countries at $2.29/min. Text messages are $.50 each and MMS are $1.30 each. YOu could most certainly beat those rates from a local provider, and with using a callback service, maybe much cheaper that what they could offer you.