A team of ex-Nokia engineers in Finland has announced the Jolla smartphone, which has a custom operating system known as Sailfish. The operating system is based on MeeGo, a project Nokia abandoned in 2011 when it decided to adopt Windows Phone for its handsets. The Jolla phone, set to be sold only online, is due to be released by the end of the year, said Antti Saarnio, chairman and co-founder of Jolla. He acknowledged it will face stiff competition but looks to carve out a niche in the smartphone arena. "For a couple of years we haven't had anything really interesting in the mobile phone market," he told the BBC. "This creates opportunities for newcomers to come in. It's different, but it's purposefully different." One different feature is what Jolla is calling "The Other Half": interchangeable back covers that will modify the operating system's interface depending on the cover chosen. Such a custom change could be team colors for a sports team, Saarnio said. "You connect it to the phone, and the user interface reflects the players and colors of the team." "It's an interesting way to show you 'belong' with something," he said.