Goto Mobile Calculator - callcosts.ie

This is run by ComReg and see who offer the best deal for your usage, if you have a contract phone and have this more then 12 months simply port the number (this takes about 2 hours) you'll get a new contact for 12 months with a different network if they are cheaper and you'll also might get a new phone for a cheap price if needed.

I move my contact all the time to get the best offer after 12 months and also get a new phone