We will be traveling in Canada in about a week. How can I be assured that my Verizon phone will work there (although I paid for international minutes through AT&T, it didn't work, which is why I am now a Verizon customer instead). I need an solid answer, please. Do I need to purchase a plan? If so, can I purchase a certain number of minutes, or a month's subscription? If so, how do I manage this? Thanks!