My wife wanted an Android slider (HW Keyboard) phone. She found this LG MyTouch Q at T-Mobile. As long as you have a WiFi signal such as in a hotel, you can make phone calls without a carrier signal anywhere in the world. It does this automatically without going through Skype or another VoIP.

Its Wifi Calling from T-Mobile. You will be able to get SMS but not MMS during Wifi Calling. and yeah its free even when you are in overseas.

Other phones that supports Wifi Calling: Samsung GS II, LG G2x, etc. Google Phone brand e.g. Nexus 1, galaxy nexus does not have wifi calling though.