As North Korea marks the birthday of its former leader, the late Kim Jong-il, there is still great uncertainty about the direction in which his son and heir, Kim Jong-un, intends to take the country – but if he aims to breathe new life into the economy, he will find foreign businesses keen to exploit any opportunities.
Chinese manufacturing companies have also been investing in special economic zones (SEZs) – set up as self-contained bubbles of capitalism along the North Korean-Chinese border.
Tor was in his early twenties when he and his colleagues set up their jeans production in Pyongyang.
"In North Korea it can be really, really hard," he says. "Sometimes you're totally in the dark, and you don't know what's going on. Sometimes you're disconnected from the people who have the actual power. You just have to be persistent and hope for the best."
After the launch of Noko Jeans at a Swedish department store in 2010, a media uproar caused not only the Swedish retailer, but also the North Korean manufacturer to cancel their agreements with Mr Kallstigen's company.
North Korea does have some key things going for it, though, including a cheap, highly literate and disciplined workforce, and low labour costs.
"Minimum wage in Rason's special economic zone is about $80 a month," says Andray Abrahamian. "In Gaesong, it's even less, around $65 a month. In China, the cost of labour has been rising, so that's the advantage."
But, says Paul French, the ravaging of North Korea's economy in recent years has meant less and less left in the country to build from.
"If you go to those border towns along the Yalu River, on the Chinese side, all you see is timber and copper wire and bits of old scrap metal that used to be machines. They're coming out of North Korea and being sold for pennies to Chinese scrap-metal dealers. You're looking at a wholesale 15-year process of asset-stripping the entire country."
The question now, he says, is this: "If you went down there [to North Korea] and signed a contract, is there anyone left sitting there with a factory who could switch the lights on and start the machines running again? I doubt that very much now."