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International Cell Phone Plan in AT&T?

  i live in Canada and going to Mexico next month for fifteen days on an official trip. My concern is that for being in contact with my friends and family while in Mexico will charge me a lot. So I am looking for some International cell phone plans for my AT&T mobile. If any one of you know any such tariff plans in AT&T cell phone which reduces the call rates and rental charges while being in international roaming then please do shear with me. I need some free international calling minutes.