The South Korean government (owned by Samsung) has been blocking and putting up barriers to foreign phones for years, including delaying the introduction of the iPhone to South Korea, to give Samsung and co. a chance to develop competitors. I'm glad to see the US government blocking a South Korean product for once, if that is indeed what is happening.
I can do the work for you, South Korea for instance banned the sale of games inside the app store for a long time. I have a hard time finding examples where South Korea outright banned phones however.
Even if they did, why would you want the US to follow such bad examples. These policies are not healthy in the long term for a variety of reasons.
South Korea is a rather protectionist country, and drawing a line between the Chaebols (Huge conglomerates such as Samsung) and the government is often hard. By the way, this is not surprising considering South Korea was a US-backed and sponsored military dictatorship for a long time.
However, the iPhone 3GS launched in South Korea 3 to 4 months after its introduction to Europe and the US.
Nokia was active there for years.
Last time I was in Seoul, the new iPad launched to great fanfare.