Mobile data is used when your mobile connects to the internet and you are not using a WiFi service at home, work or other public places e.g. when receiving an email, using Facebook, updating apps, operating systems or widgets; or making a Skype call when you are not on WiFi.
If you use all of your monthly data allowance from your plan, any additional data used on the Sure network is chargeable on some old plans, but new plans won't allow you to get any bill shocks.
Data used when connected to WiFi is free.
See our full pages for how much data you have, how to turn it off and how to keep your data bills manageable.