If you gave a fake number you would not be able to complete the sign-up. For example, when you sign up for myspace Phoneconfirm.com calls your home phone number (based on your input) and an automated voice reads a PIN number over the phone. You would then need to input that correct PIN number into a field on the myspace profile sign-up screen. If you gave a fake phone number, obviously you won't get the call
I went to the website but I'm not completely sure how it works. When you sign up the site calls the number you provided?
Yes. If that phone number was associated with underage users, harassing or sexual pradators etc ... it would be flagged and couldn't be used for further sign-ups. Think of the process of having a phoneconfirm on myspace as a bit like a library card -- phoneconfirm is a basic identity process that helps serve to create a social contract of accountability on myspace and other social networking sites.
I think the "library card" identity confirmation process is a good middle ground -- using a kind of "soft" identity confirmation system like phoneconfirm on myspace -- that isn't as vigilante as perverted justice, nor as much of a regulatory hand grenade as US Rep. Fitzpatrick's bill, and isn't as mayhem producing as as the current status quo.