Roaming should already be activated on both your account and your phone, but it's still worth checking. To check that roaming's activated on your account, log-in to the iD Mobile app or My Account online, go to 'My Services' then 'Roaming'. If it's off, toggle it on.

Hi @Giovanni Battimiello 

Roaming is typically already on by default on your iD Mobile account, you’d be able to enable/disable it via your iD Mobile app/website account.

Your device may have separate settings to enable/disable.

Thanks for the help on this @WelshPaul.

Tom