Which VoIP provider has best plans to call to Mexico?

I am looking into VoIP because my husband calls his family in Mexico quite often. I have investigated prices and I know that I don’t want to pay by the minute. Vonage and ITP have monthly rates for "unlimited" calls to Mexico, but the fine print says charged by the minute. The idea is supposed to be to save money.

Does anyone know which company and plan are the best for calls to Mexico?

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