Mine is all over the place. If I travel for work I use cellular a lot, it jumps up to 15 -20 GB range. If I am not traveling I have wifi so my usage drops well below 5 GB. I'll say an average of 10, but that may be high.
Thank God I'm still grandfathered in on the at&t unlimited data plan, cause i was using 60 plus GB a month! I had a 2 hr commute each way into the city to work for awhile and would listen to streaming music or watch netflix and surf the web. My job also didnt have wifi and i'd use cellular all day. If i didnt have the unlimited plan, i'd be paying $600 or more a month!
But now i work out of home, so i don't use cellular as much since i have strong wifi at home. Still, its nice to have the unlimited cwllular plan for when i travel. I will never let my unlimited ipad data plan lapse. I even got rid of my phone the last couple years. I may get a new iphone this fall. But i mainly want it for the mobile camera. Was wondering if i could put the ipad data sim into the iphone? But i doubt it.