Use a 3 UK SIM in Ireland?

[andy]

Strangely it has some calls cheaper than at home.

A Three UK SIM roaming on Three Ireland can call UK landlines and mobiles for 10.2 pence a minute, and free incoming calls.

So do a manual search and select 3, and 3g only.

If you want a SIM for cheap int'l calls, you might look at Tesco Ireland (a supermarket)