My plan includes no data usage. But I just found out that I have used 20KB of data. I have been using wifi the entire time and never checked "Mobile Data". So how did this happen and how does this affect my bill?
If the person who activates your phone for you doesn't turn off your data quick enough you might get a small amount of data used. Someone previously said that when they activate a phone, they turn the phone on without putting the SIM in so that they can at least get to the menu where they turn off data and activate WiFi (if the retailer has it). That way if the phone does try to use any data, it won't have a SIM card (ie your account) to charge that data to.