Check out how they manufacture and test phones at the 3Gnet Shenzhen headquarters.
Also watch my other videos in my series "Shenzhen Behind the Scenes":
1: Hongda Factory tour
2: utopiacn, Apad Android Tablet maker
3: Richtechie.com, Freescale i.MX51/53 PCB designer
4: Walking around the Shenzhen smartphone market
5: 3Gnet Factory Tour