It's available online now, again.
"Thank you for contacting Costco.com.
The Samsung Galaxy S2 for AT&T is currently out of stock on our website. We do expect to have it in stock again sometime today or tomorrow. The wireless kiosks in your local Costco warehouse are scheduled to begin stocking device on or around October 17, 2011."
"Thank you for contacting Costco.com.
The Samsung Galaxy S2 for AT&T is currently out of stock on our website. We do expect to have it in stock again sometime today or tomorrow. The wireless kiosks in your local Costco warehouse are scheduled to begin stocking device on or around October 17, 2011."