It should just work if you're in a Guido membership. It won't work if you're on any other membership. If you're on Guido and calls/texts are working but data is not then check the internet settings and if the APN field has changed from 48months.liffeytelecom.com to something else then edit it, change it back to that, save the settings, reboot and see if data starts working. If it doesn't then you'll have to contact 48 support for more assistance (see the link in my signature below). Unfortunately this is a common enough problem for people roaming in the EU on a Guido membership even though it should just work.
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.