Also you cannot call emergancy numbers on skype so id not recommend it as a indpendant means. The quality has been superb for me though both on 3g and wifi.
In Europe you can call emergency number like 112 (its the same like 911 in us) even without sim card. I think that this is not a problem at all.
Why not combine google voice with a free US voip number? I'd suggest gizmo but I think that's stll closed. Should be cheaper than Skype given that google voice does free calls in the US no? Then you can set your google voice number as your main contact and it can fall back on another number if you don't have wifi service.
