I have an unlocked iPhone 6 and a Koodo SIM card/phone number. I thought I could buy a TracFone SIM card/phone number for travel in US, and switch between the two. The TracFone SIM activated on Verizon in the US, but the signal immediately goes to "out of service" and I can't use the phone.... I am in the US now and attempting to get Tracfone to work. Is this method supposed to work? I was told it would by an Apple salesperson, so... what is wrong or what do I need to do?