Hi Karen---I believe that you and I discussed this several months ago on this site.http://www.tripadvisor.com/ShowTopic-g186591-i88-k4805042-Cell_Phones_one_more_question-Ireland.html#35898726
Hopefully the link I pasted will function.
We add some sort of international plan to our AT&T iPhones each time we leave the country and I had the original 1st G iPhone until I finally got the new one this fall. (Verizon iPhones did not have GSM and therefore could not be used in Europe.)
The rates and included bandwidth vary by country, but I am fairly sure we paid $50 for 50MB of data, plus 99 cents/ min of phone calls and a flat $10 for 100 texts. I only texted within Ireland with family members. Texting seems even more popular in Ireland than in the U.S.
As with all things cell phone related, everyone seems to have a different payment plan so worth investigating. We traveled to London and then Ireland on the same trip, so it was easier to have our own phones working as soon as we hit the ground in London so that we could contact the car service. On an earlier trip to Ireland, I just borrowed a top-up phone from my aunt, but we have become too connected to our own phones now.