I'll assume you're not from the UK or Ireland?
If you use a mobile phone and wireless internet which you purchased in the UK in Ireland you will be liable for roaming charges, which cost a lot of money, particularly wireless internet. I suggest you get separate sim cards from Ireland to use here, so you need to get a sim free phone and a sim free wireless modem you can swap, depending on where you are. There are many mobile phone shops in Ireland, so drop in and explain what you need.