I have the cheapest data plan on att which is 200mb of data. I know it isn't much, but all I can afford. It has been one day and I haven't even used the phone out of my house and it already has 10mb of data. Anyone know what I can do?
Disable data over 3G if you have wifi access, or if you don't have wifi access, disable all live tiles, disable Facebook integration, disable GPS features, disable automatic backup and uploading pics to Skydrive.
So your best bet is to turn off data Connections in Settings -> Cellular and use Wifi when at home/office. Turn on cellular data as required while on the road/home/office.