There is a separate network at ATL that is run by the airport itself. It is a pay service, but if you really have work that needs to get done you are not totally lost (assuming the SC is still down). By this time next year the ATL internet is supposed to be free (per Chris McGinnis at theticket.com)

The T-mobile SC internet was no ball of fire and I would never rely on it for getting any critical work done. I hope the new system is better.