Whats the difference on prepaid sim cards and regular att sim cards?

i want to buy a sim card on ebay but most of them look like if there pre paid sim cards from pre paid phones and if u put one of those sim card in a regular phone it gives you limitations i want to know what to look for so that i buy a regular sim card not a pre paid sim card

Whats the difference on prepaid sim cards and regular att sim cards?
why buy one on ebay? go to your cell store and tell them you are having problems with yours, and ask them to give you a new one. that's all I did. it's free. even when I ordered new service and used an existing phone, they sent me one. I just had to pay postage. the problem with sim cards is that they are attached to a phone number. if it's a prepaid card that hasn't been used in a while, or the service has expired, the service doesn't recognize the card and you have to call your company to tell them you have a new card, and to activate it against your account anyway. easier to just go to the store and have them do it for you while you are there.