While using the SubAssistant app, the only time data is used is when push notifications are received and when you open the app to view jobs or settings. Even then, the amount of data used is tiny, along the lines of a few MB, or less, per month. To put this into perspective, your data plan is likely a number of GB (gigabytes) per month and one GB contains, roughly, 1000 MB. Therefore, if you had a 1 GB plan, SubAssistant would use about 1/1000th of that data plan.