Roku tech support wanted me to change the DNS setting on the router, but you cannot do that with the 2Wire router. It's set by AT&T.
FWIW, I have AT&T U-verse service, and it works just fine with my Roku (though I've never tried a wireless connection, just a wired one).
DNS sounds an unlikely source of the problem. Can you stream Netflix on PCs (wired or wireless)?
I suspect that you can reset the DNS settings if that really is a problem. Point a browser at the 2wire gateway (should be at 192.168.1.254) and see what you can do. Admin password ought to have been given to you, but I think it defaults to the serial number of the router.