Don't think that 48 supported roaming data back in April?
Anyway all you need to do is make sure that you're on a Guido membership for your trip and everything (calls, texts, data) should just work.
If you have a non Guido membership that doesn't expire untill during or after your trip then contact 48 support and they may be able to start a Guido membership "early" in time for your trip.
If you're roaming in the EU on a Guido membership and data doesn't work straight off but calls and texts do then check your internet settings, if the APN field has changed from 48months.liffeytelecom.com then edit it, change it back to that, save the settings, reboot and see if it starts working then.
If not then you'll have to contact 48 support.
See the link in my signature below.
Unfortunately some people roaming in the EU on a Guido membership don't get this working effectively though it should.
Hope this helps.
I am not a 48 employee so if you need to contact 48 support then use option 3 or the chat facility
here.