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To setup 2 factor auth, you have to give them a phone number that you can receive a call or sms on, I believe.

I'm pretty sure that's just for recovery. The actual setup involves scanning a QR code in the Authenticator app, which is the seed for the TOTP - http://en.wikipedia.org/wiki/Time-based_One-time_Password_Al...

Yes, but they show you that QR code only AFTER you gave them your phone number and typed in the confirmation code.

Which is why I provide my Google Voice number for this purpose. Works perfectly!