AT&T phone users, How To Change Phones?

if i buy a phone on ebay, can i change the SIM card so that that phone will work instead of the old one?AT%26amp;T phone users, How To Change Phones?
The beauty of GSM networks...its all in the sim. Put the activated sim card in the new phone, and vola. Your new phone is good to go.AT%26amp;T phone users, How To Change Phones?
www.att.com. you can do it on there site or you can purchase a new phone online, like ebay and just swap out the cards.AT%26amp;T phone users, How To Change Phones?
Just put your existing SIM into the new phone.

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