I have been traveling international once a month (except for the last year) for the last 21 years. I carried two phones, because I had verizion. Got an unlocked phone that worked with sim from Monoco. I then got a local sim in the country I was in as I would be there for two weeks or more. Finally moved over to T-mobile, and use one phone now. I always buy an unlocked phone at the local Apple store. I read the Wiki on prepaid here on flyertalk. There used to be a website on prepaid sims, but it has died. I hope this helps.