It's years since I've done this and I don't know the current situation but I think you can get an eircom chargecard and use it from public phones in France by calling 0800 990 353 and entering the card details at the prompt.....
One bit of advice you'll need to buy call cards there in a tabac or somewhere else (unless the eircom cards work like another poster said) which is annoying and then type in the number on the back of the card, but first must ring a free phone number which is sometimes, dont know if always, 4 digits long dont really know about the cost sorry
You can call Irish landline nos. for the price of a local call and mobiles for 33c/min via [broken link removed] (no connection or experience to declare, and I'm sure there are lots of there, too).