Matt, What about someone who travels for most part of the year , in my case working out of asia for larger part of the year, but US being my home base. I could put my US cell phone (which is deactivated for most part of the year - like this year my cell will be deactivated for the whole year except for 2 months). I don't carry a permanent cell phone in Asia.

How could the 2 step authentication help me - say I register with my US cell phone and I am out of the country for most part of the year?