I did the DNS primary and secondary as stated and did not work for me. Then tried wired connection, no luck. Turned ps3 on and off, nothing, tried everything multiple times, manual entry and automatic.
Yeah, I was having this issue too. It's looking like At&t is having an issue with their domain name servers, but this is a pretty easy thing to fix. All you have to do is change the dns in your PS3's internet connection settings to open and that's it!
Here's how it's done:
Go to "Internet connection settings"
Select "custom" for connection method
For Wired connections: select wired connection, select auto-detect, select automatic for ip address settings, dhcp host name "do not set", for DNS SETTINGS select MANUAL and then put in two numbers from the following website http://theos.in/windows-xp/free-fast-public-dns-server-list/,choose the top option for everything else and then try signing into your PSN account.
For WIRELESS connections: select wireless, select enter manually, for ssid click to the right, click to the right for security, click to the right for security key, automatic for ip address, do not set for dhcp host, MANUAL for DNS and then enter two numbershttp://theos.in/windows-xp/free-fast-public-dns-server-list/,choose the top option for everything else and then try signing into your PSN account.