In Russia, most social networks these days require that you sign up with a mobile number. You cannot start using your account without receiving an SMS verification code.
There are in fact significant demographics - children and the elderly - where cell phone adoption is rather low. Ironically enough, these are the very groups where enhanced security measures may be most useful.
Actually no, I can't think of anyone. Buy an iPod Touch and install Google Authenticator, you will have all the inconveniences of not having a phone but enjoy the security benefits of two-factor authentication.
[1] http://yubico.com/totp [2] http://zetetic.net/software-onetime
But 2-factor does mean there in an expectation you will have to carry some kind of token device.
What's weird is that Google even sort of supports the numbers-on-paper approach, but for some reason they limit it to 10 numbers.
edit: Hmm actually thought of a possible solution. Looking into how hard it'd be to port the Google Authenticator to a non-mobile platform so I can run it on my laptop.
edit2: Although it looks like you can't enable the Google Authenticator method without first enabling the SMS method...
Just install an android emulator, e.g. YouWave, and use that virtual android device to run GA.
http://en.wikipedia.org/wiki/Google_Authenticator#Implementa...
I'm not sure about this (it was a while ago when I installed it), but I know you can install it on a new device after previously having it installed on another device (which disables it on the first device) without an SMS.