You cannot set it up with BT Mobile (unless you are with BT Business Mobile) as it requires an eSIM which currently only EE, O2, Vodaphone and Three provide service for in the UK. BT Mobile appear not to be planning to launch this for consumers which in my opinion is very short-sighted. From my brief search for information unless you are a very heavy user of data, the best option is 02 where you can add a watch data plan to an existing (or new from £8pm) pay monthly plan using the same number for an extra £5pm and it seems you can only do this from an 02 shop and not online. I am currently considering ditching my BT Family to move to O2 for this reason.
