I have an idea! How bout this instead. You go ahead and block VoIP. Sure, it's un-democratic and it's not your free market policy that is typical of democracies. Sure it makes South Korea look more like communist North Korea, but hey, if you want to block VoIP, go right ahead. It's your country.
Oh, but did I mention that in exchange for you doing this, our country is going to ask you to pay to host the U.S. troops (billions of dollars per year) that are protecting your country. Even though the costs to station U.S. troops in South Korea is vastly more expensive than soldiers calling the U.S., it still sounds like a fair deal to me. After all, we've only been paying for your protection for decades. About time you paid us back for our treasure and blood spent on your soil.
I'm sure once Americans find out about this outrage, they will offer to donate funds to U.S. military personnel stationed in South Korea to pay for the exorbitant phone charges you will charge. I'm sure the outcry from the American people will cause Congress to act and offer some sort of monthly stipend to pay for long-distance phone calls, which will now be forced to be carried by South Korean companies.
Perhaps you have forgotten about the blood, sweat, and tears shed by Americans in the Korean war?
Maybe this picture will refresh your memory...
"Bitter cold, Bitter fight" a weary U.S. Marine in Korea 1950