Samsung’s Ultra Edition 6.9 (X820 bar design) and Ultra Edition 9.9 (D830 clamshell design) cell phones, which are the thinnest yet among its form factors, leverage Agere Systems’ chip packaging design. 
The technique is called package-on-package (stacking) in which a packaged memory chip is stacked on top of the baseband chip package to reduce the overall area footprint. This enables single-sided component mounting so the phone itself can be made thinner in depth. Typically, cell phones have chips on both sides of the circuit board, making the cell phones thicker.
The Ultra Edition 6.9 (X820) measures less than one-quarter inch in depth (6.9 millimeters) and weighs only 66 grams. The Ultra Edition 9.9 (D830) measures 9.9 millimeters thick. Both are the world’s thinnest of their types, according to Samsung. The cell phones contain Agere’s Sceptre HPE 2.5-generation GSM/E-GPRS chip set.
http://www.agere.com
