GMail users can now make free phone calls (within the usa) right from their email account age. Just go here to download the deb file.
Google Voice users who have their own google voice phone numbers can also receive calls from their gmail account. Sounds interesting.
I do have a Google Voice account and making calls to Europe have all been unsuccessful for me from the USA. Be careful on making purchases for call time as Google will not offer any refunds (I lost $10) and will not respond to ‘google voice’ complaints.