Most trips start at Dublin Airport. The smart move is to install the eSIM at home and switch it on once you land. Your phone picks up Eir as soon as you turn off airplane mode, so you can order a taxi or a Bolt ride before you even reach the bus.
Dublin has the strongest signal in the country. You get fast 4G and 5G across the city centre, from Temple Bar to St Stephen's Green to the Guinness Storehouse. For a short city break of two or three days, the 1 GB for 7 days plan at $1.29 is often enough if you use hotel and cafe wifi for heavy stuff.
Cork city runs smoothly on Eir. You will have good data in the English Market, around the university, and out at Cobh where many cruise ships dock. Maps and ride apps work fine here.
Once you head out toward Kinsale or the smaller harbour towns, the signal stays usable but drops in pace on some back roads. A 5 GB plan covers a week of maps, photos and light browsing across the south with room to spare.
Galway is a great base and the network holds up well in the city, from Eyre Square to the Latin Quarter. Buskers, pubs and food stalls keep you busy, and your data keeps pace.
Galway is also where many people start a longer western trip. If that is you, think about a bigger plan now. The 10 GB for 30 days plan at $5.99 is a solid pick for anyone touring for a few weeks, since you will lean on maps far more once you leave the city.
This is the part of Ireland where signal gets honest. Along the main route through Clare, Mayo and Donegal you will usually have data, and the Cliffs of Moher are well covered. But the road dips in and out of valleys and headlands, and on the most remote stretches the bars fall away.
The fix is simple. Download your route as an offline map before you set off each morning. That way a quiet patch near a cliff or a beach does not leave you guessing. Your data comes back the moment you reach the next town.
The Ring of Kerry, the Dingle Peninsula and Connemara are the postcard parts of Ireland. They also have the patchiest mobile signal. You will get coverage in Killarney, Dingle town and Clifden, and on much of the main loop, but expect gaps on the high passes and remote inlets.
Plan for this rather than fight it. Save your bookings, directions and a few playlists offline before you drive out. When you do have signal, a 3 GB for 15 days plan at $2.10 is plenty for checking in, sharing a few photos and looking up the next stop.