You can place a Google Voice widget on a Facebook Fan Page or Business Page; doing so allows people to call you directly from the site. Google Voice allows you to create a Flash-based widget that you can embed on any website that allows Flash objects. To get a Flash object on Facebook you must be using a Facebook Page; personal profiles do not allow embedded objects. You must also use an app that allows you to embed code, such as the IFrame App, Static HTML or Wildfire.
Browse to the Google Voice website and log in with your Google Account.
Click the gear icon in the upper right corner and select "Settings." Choose the "Call Widgets" link from the options across the top of the page.
Click "Add a New Call Widget," give a name to your widget, set the options you want -- including which phones the widget should ring -- and click "Save."
Select the code next to the new widget you created and press "Ctrl-C" to copy it to your computer's clipboard.
Browse to Facebook and log in with your username and password. Search for an app that can handle iframes -- inline frames that can embed HTML code within a host Web page. Some options are IFrame Apps, Static HTML and Wildfire (see links in Resources). IFrame Apps gives you the ability to "like-gate" your content, which requires people to like your page before they can see the content on the iframe. Static HTML is simple and free. Wildfire is designed to help in running Facebook Page contests, but can also embed widgets like the Google Voice one.
Install the app to your account. Note that the app will be installed to the Facebook profile that manages the page where you want to embed the Google Voice widget. You cannot install an app directly to a Page, though you also cannot use the iframe apps on your personal profile.
Select the Facebook Page where you want to embed the Google Voice widget. Choose the option in your app to enter HTML code. Paste in the code you copied from Google Voice by pressing "Ctrl-V." Save the widget and it appears as an icon at the top of your Facebook Page. When users click on the the icon they will see your Google Voice widget, where they can enter their name and number to initiate a phone call with you.
Using the Google Voice widget allows people to call you without requiring you to release your phone number.