The Guinness World Records named the Modu phone as the lightest cell phone in the world. At just 1.5 ounces and 2.8 inches by 1.4 inches by 0.3 inch, the Modu is a full ounce lighter than the already miniature Pantech C300. Without a doubt, it's the tiniest cell phone I've seen outside of Zoolander.
In case you're not familiar, Modu is a modular cell phone that can be placed into "jackets" that change the both the appearance and the functionality of the handset. The Modu only has a tiny display, a couple of navigation controls, a mini USB port, and a charger jack. It's a normal cell phone in most respects but you're not really meant to use by itself. Instead, it's designed to be inserted into one of the jackets, which basically are the shells of a larger candy bar phone. My Modu hands-on from the GSMA World Congress will give you the full report.