Technically you can add a line at any place that is authorized by your provider. Now the knowledge of the sales person is what matters. Just make sure you tell them that, you want to add a line without any other change to your contract. from there, I'm sure you know how to switch the S4 to your unlimited line, as it has been discussed many times here.This may be a stupid question. Can I add a second line at walmart and do the switch so I dont lose my unlimited data? Or can I just do that at verizon stores? I have a s3 and want s4 which cost $148 @ Walmart. Thanks