If you are going to TRY to use another carrier's sim card, that is up to you what local carrier you use.
You will have to check to see what carrier is local and have prepaid services for the time you will be there (just as if you were going to sign up for prepaid service while in the U.S. you could choose Verizon, T-Mobile, Sprint, AT&T etc...) Most carriers that offer service have a prepaid option, but it is really going to be up to you to look to see what carrier's have the service you need at the price you would like for the areas you are travelling to.
Myzee, we want you to stay connected everywhere you go. What countries are you traveling to? How much do you plan to use your Jetpack? Have you explored the international options with us? This is a great place to start. http://spr.ly/6585Dcu5z;
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