When you are logged into your Google Voice account, you go to settings and one of the options is to copy the code for the CALL ME widget. The CALL ME widget, when clicked, allows a user to key in their phone# and Google Voice connects the caller to you at the number you specified in your settings.
logged into your Google Voice
copy the code for the CALL ME widget
I use it on my website - clients from North America can call me toll-free. Prospective clients that don't want to share their phone# don't have to. It can be anonymous.