I don't use data much at all, just background apps like email, news etc. When I was with O2 my usage was around 200Mb/month but since joining PlusNet it's dropped to only around 20-30Mb/month. I haven't altered any settings on the phone, no fewer apps or anything. I wonder what O2 was doing to cause my data usage to be so much higher
Democracy - 3 wolves and a lamb voting about what to have for lunch!
One thing you can do is go into the phone and look at the cellular data usage. Log what it is (or reset it) and check again in 2 weeks to see if the usage on cellular (excludes wifi) matches with the plusnet view.