When you move to Ireland, you should consider changing your mobile phone provider. If you continue to use your mobile from your home country, you may be charged expensive international roaming rates.
The main mobile networks in Ireland are:
You can compare charges and tariffs on each network online at callcosts.ie
If you already own a mobile phone, it may be possible for you to just buy a new SIM card. This will only be possible if your phone is unlocked. If your phone is not unlocked, you will need to purchase a new mobile phone. Visit a large shop like Carphone Warehouse and you may get a good deal on a new phone.