Four years after their launch, tablets remain overwhelmingly stuck at home and connected by wifi, frustrating mobile operators who are deprived of a potential new source of revenue. At the February 24-27 Mobile World Congress in Barcelona, Spain, manufacturers such as Japans Sony, Chinas Lenovo and Taiwans Asus again unveiled a range of new tablet models, now considered essential to their mobile device offerings. Sony Mobile revealed its Xperia Z2, proudly describing it as the worlds slimmest and lightest waterproof tablet. It is perfect if you want to take it into the bathtub, to the beach, to the pool, Sony Mobile official Almos Szabo said at the Japanese manufacturers stand in the worlds largest mobile industry fair.