Remove the SIM card and unregistered it from the find my iPhone and iMessages.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
Theeaterofshades, we want the sale of that device to be successful. You will also need to disable, "Find My iPhone" on that device, as well. Click http://apple.co/2yzBGuC for the steps on how to do this.
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