Hello again, Ronnie! :)
There is a
Spar in Terminal 2 at the Airport where they offer the option to buy a Sim Card. Make sure that your phone is unlocked!
If you'd like a bit more choice between different providers, you'll find loads of mobile phone shops in Dublin itself, or simply go to one of the many Tesco's along the way.
Pam recently visited us and added some helpful tips about using your mobile phone on the Emerald Isle in
this thread about her trip as well.