Get an Unlimited Europe calling subscription from Skype – £2.95/month. ( or equivalent in Euros)
Once you have saved the number, you’ll receive a text from Skype with a local number( you can specify your neareast locality).
I have just discovered that Tesco Mobile( who – as far as I know ) now have the best International rates, and it’s all prepaid, so no contract etc.
You can simply order a sim, and as long as your phone is unlocked, you can use it straight away. It might come in handy even if you are visiting Ireland ( and assuming your phone is unlocked).