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...
http://en.wikipedia.org/wiki/Google_Authenticator#Implementa...
Just install an android emulator, e.g. YouWave, and use that virtual android device to run GA.
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.