Google Voice just charged me (USD) $0.40 for 30 minutes of calls to landlines to check that my London-based family was OK (answer: yes). Great value. If I had called mobiles, it would have cost $2.00. Again, great value.
Easy to set up and only asks for a $10 credit to get going. I strongly recommend if you have long-distance calls to make. It is greatly cheaper than PCCW, SmartoneVodafone and cheaper than Skype to phones.
As with any internet-based telephony, don’t be downloading substantial updates while chatting, the quality goes to pot.
[Update: some more information from Engadget]