3G is a radio technology used for both voice and data. In other words, 3G is NOT just about the Internet. In fact, phone calls are also placed over 3G and usually there is better call quality and reliability over 3G. (Quality obviously varies based on the cell towers in the area). The 3G toggle in the Android settings of GSM phones will cause the phone to fall back to 2G for both voice and data.

Many users confuse “3G” with mobile Internet. They think disabling 3G prevents their phone from using the Internet. For users looking to disable mobile Internet on their phones, please search for “APNDroid” on the Android Market which offers a plug-in for Locale.

There is also another plug-in called the “Locale Mobile Data Plugin” which contains a condition for detecting Internet usage as well as a setting for disabling mobile Internet over the cell network.

While Android claims that switching from 3G to 2G will save battery power, this is not a huge savings. While actively browsing the Internet, 3G will likely require less power because it is faster and it will take less time to find something.

For users really wishing to slow down their Internet connection by switching the 2G/3G setting on GSM phones, there is also the Toggle 2G app with a Locale plug-in on the Android Market which requires the Cyanogen ROM in order to work properly. Note that toggling 2G/3G in such a manner will disrupt the phone entirely (voice and data) for about 30 seconds during the switchover. For users running stock versions of Android, this plug-in will not work and it is absolutely impossible to toggle the 2G/3G setting.