Mobile phone companies on Monday began unveiling the latest in smartphone technology at this week's Mobile World Congress in Barcelona, Spain.Sony announced its new Sony Xperia Z2, a slim and waterproof premium Android smart-phone designed to take on Apple's iPad Air.The device, which features video recording technology in 4k resolution on a mobile phone, is the newest addition to Sony's premium Z series and launches globally from next month.Kunimasa Suzuki, President and Chief Executive of Sony Mobile Communications, said: "With Xperia Z2 we have taken our premium Z series to the next level."South Korean electronics giant Samsung is set to unveil its new Galaxy S5 smart-phone, which is also said to feature 4k resolution video recording, a finger-tip heart rate monitor and a 5.2" display with 1080p resolution.Nokia has also unveiled three smart-phones dubbed X, X+ and XL, which use Google's Android operating systems, for emerging and budget markets.The Nokia X devices resemble the company's Lumia range of Windows Phone smartphones, sporting bright colours and a plastic body.Facebook's Mark Zuckerberg is expected to tell the congress that he wants to "connect the unconnected" and bring internet access to millions more people worldwide.Wearable technology is also set to feature at the event, with not only "smart watches", but also shirts embedded with mobile technology that can gauge the wearer's temperature and pulse rate through the material.PW