[justlearning]

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?

[Matt_Cutts]

What evan_ said: you're using the phone as a pocket computer, not as a phone. You don't need phone service at all--the authentication program will run on your phone even if you don't have service or you're in a foreign country.

Enough people have asked these (very reasonable) questions that maybe I should do a video about two-factor authentication.

[stumm]

This video made by Google is pretty good and covers many of the concerns people have: http://www.youtube.com/watch?v=zMabEyrtPRg

[Matt_Cutts]

Nice--you're right, that video covers pretty much everything!

[evan_]

You don't actually need to have cell service- there's an iPhone app (and presumably apps for other platforms) that lets you just generate new codes at will. You only need internet access to set it up initially, and you can do that with wifi.

won't help you if you have no phone at all but you can generate one-time-use passwords at will, so you could just stock up I guess.

[jackowayed]

Actually, it looks like you can only have 10 active one-time passwords at once.

On the page that lists the current ones and lets you regenerate them it says, "Be sure to throw away any previous versions. Only the latest set of backup verification codes will work."

[josh33]

Google voice. It was a little "Inception"-like to set up but has worked flawlessly for me. As long as you take a mobile device with you that is authenticated and you have wifi access you're golden.