I found out about the "originating from US" restrictions on this gift card the hard way. I saw that my 24-hr hold on a HKG-ORD-LAX-HKG flight did not allow me to pay with gift card, so I called to see why.
Interestingly enough, they were able to apply the gift card balance to the itinerary, but once I found out about the $25 phone booking fee, I decided against doing it over the phone.
So moral of the story ... maybe you can use these gift cards to book flights originating outside the US, but only if you call in and are willing to pay the $25 phone booking fee.