If you are an AT&T customer that is still down since the switch from the @Home/Excite network to the ATTBI network, then here is something to try while you wait for one of their techs to get back to you.
It seems a lot of people have been able to provision their cable modem themselves with no help from ATTBI. This can make the differnce between no connection and full connection.
So even if you have no connection (I assume you'd be here now via a phone modem) try going to the IP numbers listed as it has seemed to work for many people in the same situation.
Here's the thread at DSL Reports:
Provision your cable modem yourself 
Linear Mode
