It turns the radio off so you wont receive any data or phone calls. Nice for at night when you don't want to take calls and you still want to view your calendar.
You'll also get a lot more battery life if you turn the radio off. For example when I went to Bermuda, I didn't want to get charged for the emails I would be getting but I still wanted my alarm and calendar to work so I kept the radio off and it lasted all 9 days I was there on a single charge..And I still had 3 links of battery left on the plane home. So if you want to conserve battery as well you can turn the radio off.
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Cingular/8700c
-Unlimited Data Plan-which does come w/ wap.cingular access point included heh
Any Questions, feel free to PIN!
Also, to save battery.. if your in an area were it's really hard to get a connection and let say that your gonna be there for a while, it's better to turn it off. It helps you save up some battery life.