Version 2.0 of Auto3G, available in the Cydia store, has just been released. Auto3G extends your battery life by automatically turning off the 3G radio (leaving on the 2G radio) when you lock your iPhone and automatically turning on the 3G radio when you unlock your iPhone.
Version 2.0 now allows you to have Auto3G automatically turn off the 3G radio when you have a Wifi connection. Version 2.0 even enables you to keep your iPhone on 2G at all times unless designated applications are running. This way you always have the speed of 3G when you need it without the battery loss.
As explained by Apple, this results in up to 100% greater battery life: "7 hours of talk time on 3G, 14 hours of talk time on 2G." (apple.com/batteries/iphone.html)
Version 2.0 also has additional features which include allowing you to (i) specify applications that if running will prevent the iPhone from switching to 2G after it locks, (ii) specify a timeout interval that will delay Auto3G from switching to 2G after the iPhone locks for the specified interval, and (iii) default the iPhone to 3G while charging even when locked.
Name: Auto3G | Download from: Cydia | Price: 6$
[Read the original blog post]