got this txt a few days when I was up near the boarder. I've an O2 contract, not sure if it'll be the same for PAYG.
Welcome to IRELAND. You're on O2 Travel. Data costs £1.99 per day. Calls to the UK/EU cost 50p to connect, then it's free to talk for the first 60 minutes, after 60 minutes UK out of bundle rates apply. Answering your phone also costs 50p to connect then it's free to talk for up to 60 minutes, after 60 minutes UK out of bundle rates apply. Texts are 8.5p (and free to receive). Prices inc. VAT.
I think I heard about this & it's the same from most of Europe. If correct this will be handy for France etc.