Ok. #1. AT&T typically charges data MBs to your account once or twice a day. The time of day this occurs has nothing to do with your data usage or apps you may be using. It is cumulative for the past 12 or 24 hours. Otherwise, there would be hundreds of entries per day.
#2. Text messaging does not use data. It uses your voice connection. So turning off data will not prevent you from sending/receiving texts.
#3. When your phone is set to WiFi only (data turned off) it actually does turn on briefly every two hours. Still testing as to what actually occurs, but I have watched my mail accounts get updated in repeated tests with data turned off.
#4. Be careful what you wish for. WiFi always on wild be a tremendous drain on battery. With Wifi sleeping in the background, and turning on briefly every two hours, its maybe 3-4% battery drain per day. On all the time, multiply that by 10 or more.
Sent from my HTC Surround using Board Express