If you only want subscribers to be added to Call Loop AFTER they have confirmed their email address, then this tutorial will show you how to do it.
STEP 1: Create Your Call Loop Group
STEP 2: Integrate With AWeber
STEP 3: Copy Your URL
STEP 4: In AWeber hover over "My Lists" and click "List Settings"
STEP 5: Goto "Confirmed Optin"
STEP 6: Scroll down to "3. Success Page"
STEP 7: Paste in the Call Loop URL
STEP 7: Check to "Pass subscriber info..."
STEP 8: Save!
So now AFTER they have confirmed their email address will they be added to your Call Loop list.