It works automatically. You just need to make sure you’re using a compatible device with data roaming switched in the settings and the latest software installed.
Before you go, don’t forget to check you have roaming enabled on your account. Got a Spend Cap on your account? Make sure it’s set to an amount that covers the daily roaming charge, plus any other charges. If not, you may not be able to roam.
On Pay As You Go? Your SIM must be active and have been used to make a call, send a text, or use data before you can use it abroad.
When you arrive abroad, you’ll get a text confirming the charges for using your device there. You can check the standard international roaming charges for any destination by tapping the Roaming charges link in the text and choosing the destination you’d like to check.
Remember: to call or text back to the UK, you must replace the first 0 in the number you’re calling or texting with +44.