Firstly, if you are diverting all calls, make sure you do it before you leave the country - not once you get away to your destination.
Secondly, 10-15c for text messages when roaming is probably not the case. All operators charge more for sending texts when roaming.
Thirdly, one thing to be aware of, if you are using your phone abroad, when you come home, make sure you switch it on straight away when you get back.
If you arrive back, and don't, but your friends/family/etc call expecting you back in the country, and your phone is still off (even though you're in Ireland), your phone will be directed to wherever you were abroad, and then bounced back to your voice mail, costing you a chunk of money.
And this isn't a ripoff. It's just a technicality. When you turn off your phone in Spain or wherever, as far as your network knows, you're still there until you turn on your phone back in Ireland.
So, if you have jetlag, and need to recover without having your phone one, turn it on, register on your Irish network, and then switch it off again.