North Korea is evading U.N. sanctions by profiting on the soaring domestic demand for smartphones, according to defectors, experts and an analysis of North Korean-made phones.

Economists estimate as many as 6 million North Koreans — a quarter of the population — now have mobile phones, a critical tool for participating in an informal market economy that has become a key income source for many.

Reuters spoke to some 10 defectors and experts about the use of mobile devices in North Korea, as well as reviewing state media reports and advertisements for mobile devices and examining two North Korean-branded smartphones.