11-10-2015 3:26 AM
If not on WiFi, yes, data usage is charged. You should go to the Google Play store or the Apple apps store and in settings, make sure it updates over WiFi only. Only update the OS over wifi, unless you have plenty of data left near the end of the month that will expire anyway.
06-14-2016 11:59 PM
As @Gary L mentions, it can vary a LOT, from app to app.
To avoid chewing through lots/all of your data, the general rule is to do these via WiFi type connection. Obviously if you've got an app that needs an update, and only have cell access, than 1-2 shouldn't be an issue, in the big picture.
*If this (or another post in this thread) fixes your problem/issue, please mark it as "accept-solution", and I'll tag it, to make it easier for others to find the answer(s). FYI: I'm an AT&T end-user, just like most of us in the forum. Thanks.