What are some examples of why my data package is being used when I'm at home and connected to my wifi? I have an iphone 3gs and my fiance has a samsung infuse 4g (I don't know if it matter what type of phone but just in case it does) any help would be greatly appreciated. Thank you!
Unless your phone is plugged into a charger, it will disconnect from WiFi when it goes to sleep to conserve battery life. So, any automatic functions like push email while in this state will occur over the cell data network instead of WiFi, even if it is available. When you wake the phone back up, it will reconnect to WiFi. As long as it's on a charger, it will stay connected to WiFi, even when asleep.
Also, AT&T in many cases bills an aggregate of the daily data use, usually about 1-2 in the morning. If you see a listing for say 20MB of data at 2am, it usually doesn't mean your phone used 20MB of data at exactly 2am. It typically measn that you used a total of 20MB of data in the last 24 hours or so, and they just charged you at 2am.
There are a number of threads on how the phone uses data and how AT&T bills it here.
1) 15 minutes after phone goes to standby, it turns off wifi *unless* it is plugged into power. Any data you use there (push email, notifications, apps running in the background) will then start using cellular data
2) visual voicemail always uses cellular data
3) crash reporting to apple seems to either happen in the middle of the night (and fall under 1 above) or always uses cellular data
Samsung is Android - it also does background data, and like most every other battery powered device will turn off wifi if on battery and on standby after some time.