As I read Can Two-Factor Authentication Fix Mobile Security it reminded of a comical scene.
I was included in a meeting regarding a service an agency was looking to procure and it got to the point in the demonstration where the vendor was going to demonstrate the admin piece. They pulled out their cell phone so that they could complete the two factor authentication to login. The only problem being the building that we were located in is partially underground, needless to say when the info was sent to their phone that they needed for logging in they were unable to get it. One of the two vendors then ran down the hall with the cell phone trying to get far enough towards the atrium that they could get a signal while the other requested the code again. He ran back in and didn't make it back within the time allotted to enter the code, so they tried again, he ran back quicker and that time the other person was able to get logged in with the code. Just one of those things to take into account when deciding on a 2 factor solution.