Depends - if you are roaming in the EU on a Guido membership then your Guido membership data allowance and/or any data add-on allowance should work:
If you are roaming anywhere else (rest of Europe/outside EU, North America or Oceania) then data will not work as 48 don't support it other than when roaming in the EU on a Guido membership.
Bear in mind that many people have been having problems getting data working while roaming in the EU on a Guido membership even though it should work.
Also - since you seem to be using an iPhone you should be aware of this issue due to the stupid way that Apple do things - it hits many iPhone users and causes them problems when trying to get even calls and texts working while roaming:
Hope this helps.