Hi Ken,
I suggest you to buy the simcard in Italy, all other ways are not very reliable.
Wind could be a good solution, with 3G coverage in Rome, Florence and La Spezia (close to the Cinque Terre) and 2G coverage at the Cinque Terre (where no operator has perfect coverage, by the way), unless they already upgraded to 3G there too.
For surfing the net you can choose one of the data options such as Mega 1500, Mega No Limit or Mega 15000. It all depends on the amount of data you plan to use.
Vodafone Italia has an i-phone add-on for EUR 3/week offering 500MB of data per week:
http://www.areaprivati.vodafone.it/1...ack_per_iPhone
It's quite a good offer and Vodafone has wider 3G coverage than Wind. But if you have an old 2G iphone it's nothing better than Wind (which has EDGE in some places).