No, the Go Phone does not use sim cards. They use authorization numbers; which could be purchased from Wal-Mart, any convent store, Dollar General, etc…
There are two types of wireless networks: GSM and CDMA. All GSM phones require SIM cards because of the way a GSM network works. I am guessing that by "GoPhone," you mean AT&T's pay-as-you-go phone service, and AT&T runs on a GSM network, so any AT&T phones, including the GoPhones, require SIM cards.
There are several Go phones that do have a slot for a sim card. However, these phone are a little more pricey and sometimes the card may not work correctly depending on the features on the phone. So you may not get all of your data that is saved on your Sim Card.
Yes, the AT&T Go Phone does use a sim card. With the sim card you are able to use your AT&T service on any AT&T Go Phone by transferring the sim card from your Go Phone to a different Go Phone.