And the winner is the Maxi Handy (Maxi Mobile). It measures 2.05 x 0.83 x 0.45 m (6.72 x 2.72 x 1.47 ft) and was installed at the Rotmain Centre, Bayreuth, Germany, on June 7, 2004. This giant cellphone fully functional and can send and receive SMS and MMS messages. It made from from wood, polyester and metal and features a colour TFT screen. I cant image about the sound from this giant speakers? 

Largest Mobile (Cell) Phone