I think COOP Voce could be a good solution.
You can activate the "NO FRONTIERE" option for free and call all Koean numbers at € 0.15/min (plus 0.15€ set-up fee).
For data there are 4 different options, take a look here:
http://www.prepaidgsm.net/forum/ital...html#post36151
You can buy it at any COOP supermarket, which are very common in Italy.