It's become a standard recommendation on battery-related threads: Set WiFi to stay on when the phone goes into sleep mode. My understanding is that 3G is only active when data is being transferred. But when WiFi is on and connected, it is ALWAYS on and connected. Let's say I sleep for 8 hours at night, and I have apps that update every 30 minutes. Do I want WiFi to be connected for the entire 8 hours, or just let the phone use 3G for a total of 16 times (8 hours / 30 minutes)?