I encountered this when I tried to call an airline's customer support number from outside the US. I started digging around, and it turned out that such numbers only work for free within the US, but from abroad, it's almost impossible without virtual telephony. I started looking for a proper guide explaining the dialing technique and hidden restrictions. Now I understand that for businesses, such numbers can really boost trust, but it's better to figure it out beforehand to avoid overpaying and getting blocked.