I had a wonderful 2 week visit to ireland.
I had no problem in Ireland at all. You can simply buy a O2 Sim cards at kiosks all over Ireland.
Just insert it in and follow the instructions. no problem.
I also purchased a multi European country Sim card while on line from Telestial
http://www.telestial.com/sim_cards.php
The format would be: + (country code) (phone number).
>>> What do I dial while in France to a number in France? <<<
+33 (number in France). The "33" is France's country code. I did this while in Germany (Germany to Germany number) and had no problems.
>>> What do I dial while in France to call a USA number? <<<
+1 (area code) (phone number)
>>> What do I dial while in Ireland to dial a number in Ireland? <<<
+353 (number in Ireland)
>>> What do I dial to call from Ireland to the USA? <<<
+1 (area code) (phone number)
>>> What do folks in the USA need to dial when calling me? <<<
011 (country code) (cell number). Note that "011" is the international access code in the US, so whoever calls you from the US won't need the +.
All the best,
Carol