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None of the iPhone LTE phones are locked to Verizon and can be used on other compatible LTE networks GSM networks and the quickly disappearing CDMA networks. Remember even when you are here in the states most of the time you're not even using CDMA anymore with this iPhone 6s as  LTE is an extension of GSM.  Your phone will work great in Europe just make sure you have the right plan as noted above. One thing to consider is their new plan which allows you to use your own minutes text and data plan for $10 a day while traveling depending on how much you're going to use your phone that could be an expensive deal or actually a good deal