I don't know off hand.
But you can buy a 120 minute AT&T card at Wal-Mart.com for $10.00. I wouldn't think they would count that as a gift card or Wal-Mart shopping card, but I don't know. (There are other cards with other minutes. I didn't know how many minutes you were looking for.) Looks like there's shipping and handling of $0.96.
I didn't see anything specific at MyPoints, and I didn't check any other sites.