You can call home for free with your cell phone.
Just dial 1544 0044. You will hear some pre-recorded Korean giving instructions.
As soon as you hear that voice just dial your country code, area code and number followed by the # sign.
BAM! You are connected. This service appears to be 100% free, except for your normal phone charges. I have used this service for eight months with no surprise charges on my bill.
Hope this helps someone!