Apex domains cannot have CNAME records.
Question and response
Question
dig att-inc.com. NS
Answer
att-inc.com. 5 NS ns10a.attdns.net.
att-inc.com. 5 NS ns10d.attdns.net.
att-inc.com. 5 NS ns10b.attdns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0