When I was in college we used to joke about my roommate's giant "in case of emergency" Nokia phone, which was literally larger than our cordless phone. Whenever she would whip it out - often as part of her stand up routine about her mother and grandma - we would joke about it being the world's largest cell phone. I am actually shocked to say, it isn't so!
The world's largest functioning mobile phone is the Maxi Handy from Maxi Mobile, according to the Guinness World Records. It measures 6.72 by 2.72 by 1.47 feet and was installed at the Rotmain Centre in Bayreuth, Germany in 2004 as part of the 'einfach mobil' infotour.
The phone is made from wood, polyester and metal and features a colour TFT screen. It is fully functional and can send and receive SMS and MMS messages. I've never wanted to visit Bayreuth, Germany more than I do at this moment.