How do I disable or enable mobile data on my iPhone or iPad and see usage?

Find out how much mobile data you're using, and how to turn mobile data on or off for all apps or individual apps.

Note: Diocesan iPhones and iPads (with SIM) use the Three mobile tariff with unlimited data in the UK. Disabling mobile data may only be relevant if you are planning to take the device abroad and are travelling. See:
What are the details of the Three Mobile tariff on my diocesan iPhone or iPad? >