I have AT&T and my friend couldn't believe, that I can simply use any phone I want by simply swapping the sim card. I went on a camping trip, and wanted to use my old beat up iPhone 3G instead of my nice Galaxy S4, and he said "I thought that AT&T deactivated that iPhone". So I put the sim card from the S4 in the iPhone 3G via sim card adapter(Micro Sim), and he couldn't believe that it worked. He said with Sprint, he always has to go to the store to transfer service to a different phone.
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