I have an old Samsung Galaxy Ace GT-S5830D that I plan on getting unlocked for travel. Will i be able to use this phone in Ireland if I buy a SIM there?
Voice and 2G data will definitely work on any carrier in Ireland. Depending on the exact 3G frequency bands (and my search has revealed conflicting information), 3G may or may not work. If your phone has the 2100 3G (HSPA, UMTS) band, then you'll be able to use their 3G networks as well.