Cell call blocker , cellular blockers off voice
Yes, your friends are right about it. North Korea has 100 days of mourning to honor legacy of their leader passed away. During these 100 days any usage of mobile phones, smartphones and other personal electronic gadgets is strictly banned. People who dare to break this restriction will be treated as the war criminal and have very harsh punishment, starting with labor camp for many years and ending with death sentence.
North Korea is very rough country with strict behavior rules. Despite the fact that mobile phones are the privilege of not so many people there, the North Korean government might use cell phone jammers in public places to avoid violation of discipline. They have the necessary technological potential for that because they have already demonstrated what North Korea is capable of. No jokes with this country, you know.
Still, if you are living there or visiting this country as part of your business trip, I guess you definitely should hedge yourself from possible danger of cell phone ringing in your pocket to make sure that your life won’t be under threat because of that.