Cell phone

The answer depends on your carrier. Perhaps this will help you figure things out.
https://www.ricksteves.com/travel-tips/phones-tech/data-roaming

As Liz says, depends on your carrier. Maybe is it one of these? (all corrections welcomed)

AT&T - I don't think it will work unless you pay extra for an "add-on". Last time I did that, it was $50 for 30 days of international roaming in the EU. Phone worked normally, I could call/text to/from USA, and I had 15 gb. of cell data to use.

T-Mobile - Same as AT&T, except if you have a slightly more expensive "Magenta" plan, your phone will work normally in 203 countries, but you will have very slow data. In 11 countries you will have normal fast data. You can also buy an "add-on" for fast data in those 203 countries. My Magenta +55 plan costs $70 for 2 lines.

Verizon - I don't know about different plans, but many people buy an "add-on" for, I think, $10 per day (capped at $100/month), to get normal coverage. If Verizon, make sure you buy the "add-on" if you need it, otherwise huge fees add up.

Other less-expensive MVNO's (resellers) - Mostly no coverage, nothing will work. Many folks here talk about buying a SIM card or ESIM for the countries they will visit. More complicated, but less expensive than most of the "add-on's".

Except some, like Ultra Mobile (uses T-Mobile towers), will have coverage in 90+ countries (but maybe not yours), if you have the right SIM card (only available on Ebay, I think). You will be charged $3/month plus 3 cents/min. for talk, 1 cent per text, and 3 cents per megabyte. Three cents/megabyte sounds cheap, but if you do much with your phone (like Google Maps), it would wind up being very expensive. I have two old cellphones I keep in each of our vehicles as backup phones. They each have an UltraMobile sim card (bought on Ebay). One of the SIM cards claims to work the same way in 90+ countries. One SIM did not claim that. I will know more in a few months.

Vikki, you might have more responses to your inquiry if you post it in the "Tips and Trip Reports" section, under the Category "Technology Tips". There are a lot of posts about international cellphone use there. Or you could search that Category for "cellphone" and find quite a few threads.

I have Verizon and they offer two plans to allow you to use your phone just like at home

• $10 a day, only charges on the days you actually use it
• $100 a month

We used to use the $10 a day plan when our trips were short, now we use the $100 a month plan.

We have AT&T, added the $10.00 per day international plan, and it worked seamlessly for Google maps everywhere in Ireland, Northern Ireland and Italy, and for calls and texts as well. We used WhatsApp for contacts in Ireland and Italy.

Ireland is a very technologically advanced place. More advanced than most places in the US.

Assuming you have a cell plan (US or otherwise) that allows you to roam in Ireland, maps and other stuff that requires internet access will work fine pretty much everywhere in Ireland.