The open data policy does apply.
Yes, the open data policy applies to your plan. Your EU roaming data threshold is 0GB. This means you can use 0GB of your standard monthly allowance of data to roam, just like you do at home. However, if you use more than 0GB of your standard monthly data allowance abroad, you'll incur a small additional charge of 0.76p per MB. This will only apply to your monthly standard allowance; there won’t be any additional charge for using add-ons, and you can use these in the EU inclusive roaming countries just like you do in the UK.
If you do use more than your EU roaming data threshold, you'll have no additional charges in the first month. But the second month you use more than your EU roaming data threshold, we'll take the following action:
If you reach 80% of your EU data roaming threshold, we'll send you a warning text, giving you a chance to slow down.
If you reach 100% of your EU data roaming threshold we'll send you another text message - to make you aware of the situation, and give you a second chance to stop data roaming and avoid charges.
If you exceed the threshold, we'll apply an additional charge of 0.76p per MB.
Note: your EU roaming data threshold refreshes along with your allowances each month.