I ran across a little note about this phone service, jaxtr, in Wired this month. Basically, you set-up an account with them (as long as live in one of 29 countries) and they give you a widget (like the following) that lets people call you for free from their own phones.
It works just like Google’s Click-to-Call:
Click the phone icon or call link, and you’ll be invited to enter your own phone number into a special field. When you do so and then click Connect for free, Google will call your number almost immediately. Pick up, and you’ll hear ringing on the other end as Google connects you to the business you selected. When they answer, you simply talk normally as you would with any other call.
Check out all the details in their FAQ. It’s basically unlimited emails, unlimited voicemails, and 100 minutes of direct calling per month for free. Not a bad way to let people give you a call without revealing your phone number, eh?
Now, this may be an incredibly bad idea, but here’s my jaxtr widget. If you ever wanted to call me, or just leave me annoying voicemail for some reason, now’s your chance 
I’m in the Eastern timezone, so no threatening calls in the middle of the night, k? 