AT&T owns a number of domains, including SBC and Bellsouth. Some AT&T domains also use Yahoo filtering rules to send mail to the bulk folder1.
There are no published limits for connection or sending limits. I have seen claims of limits of 2 connections per IP and 30 connections per IP, but there has been no data presented for either claim.
AT&T does not offer a FBL.
AT&T does not offer a whitelist.
AT&T uses the Return Path Certified whitelist in mail delivery decisions. Mail from IPs on the Return Path Certified list will see better delivery at AT&T domains.
AT&T provides minimal support for senders. Senders who have email blocked at AT&T can follow the URL in the rejection message, or visit their SMTP errors list
AT&T also provides as block inquiry website. Block Inquiry Form
AT&T does not publish any specifics on what blocklists they use. Their email best practices page suggests that sending IPs should not be on any Real-time Blackhole list[sic] and that they may block mail listed on any reputable list.