eSIM for Republic and Northern Ireland

We were just there (Republic and Northern) and used Bcengi and Roamless Pay-As-You-Go Esims, which worked very well. Bcengi does not provide a phone number. Roamless allows you to make worldwide phone calls for 4 cents/minute, but you can't receive calls. Both of them did use the Three network, which had good coverage. So any Esim using the Three network should work fine for you.

Your choice depends on whether you want to use your normal cell number.

Last year I bought a Maya "data only eSim" ($10 for 5GB?) but for either cockpit error or my own carrier's rules, I couldn't get Wifi calling via broadband to work even though it works at home. I'm not about to learn WhatsUp or other workarounds. Others here report the data only approach works fine for them.

Since I needed something, I walked into the Three Store and paid about $20 for an Irish phone number and 10GB, which worked instantly.

I also have a GiffGaff esim on my phone which used to work in Ireland, but under new EU rules, you have to connect to a UK tower before it comes to life, then you get 60 days of EU-wide service. This would work for you if you're going to NI at the beginning of your trip.

I recently changed my service to Mint Mobile (owned by T-Mobile). It took 2 minutes to transfer my number from USCellular and I pay $15/mo per phone. Their international roaming is much cheaper ($20/10days), so my wife is using that on our Scotland trip next week while I use Giffgaff. She'll have her usual number for her social life and I'll have a UK number for restaurants, ferries, etc.

Be aware that navigating with your phone my be more than modest data. We use a dashboard GPS for the car, but usually rack up 3GB on the phone just navigating on foot for three weeks.