You must use the Windows version of Garmin Express Fit to set up wifi on your new Forerunner (tried using FR620).
For Apple/MAC OSX users, you must have a Windows computer, bootcamp or virtual machine. Here is where you get the Garmin Express FIT application that you will need to set up any new wifi network you want to connect with:
http://www8.garmin.com/support/download_details.jsp?id=6741
Garmin, please fix Garmin Express version 3.1.1.0 to allow wifi enablement or update the documentation. It is not clear to MAC OSX users that they must use a Windows application (G.Ex. FIT) to get wifi to work on their newly purchased Garmin Forerunner.