[thehickmans]

You could combine IP geolocation and caller ID phone verification. Geolocate the user's IP during the sign-up process and provide the user a code to activate their account through a 1-800. Compare their area code against the location they provided and see if they're close enough to trust.

[akalsey]

Now that long distance service is essentially free for everyone and mobile phones (and VoIP) have nationwide networks, more people are choosing not to update their phone numbers when they move.

This means that there's a good chance my phone might have a Chicago area code but I live in LA now.