One of the blackhats proposed a clever outside-of-the-box solution: 1. Create a site that promises free ringtones. 2. Once a visitor enters their cell number,

One of the blackhats proposed a clever outside-of-the-box solution: 1. Create a site that promises free ringtones. 2. Once a visitor enters their cell number, forward it to Craigslist, who sends a verification call to that number. 3. Ask them to enter the verification code on your ringtone site. 4. Redirect the verification code to Craigslist, and send your visitor a ringtone. This is how CAPTCHA's got cracked as well: by embedding them into porn. ("Would you like me to take off my dress? Enter this code") It sounds hard to beat. Any other outside-of-the-box solutions that you can think of?