Prepaid data in Italy is great, very competitive and fast, especially with TIM.
I don't know about calling or texting back to the US though.
I have a T-Mobile phone and use a prepaid SIM for unlocked devices like iPad and a older iPhone.
But I don't get a prepaid SIM if I'm only in a country a couple of days.
For Italy, TIM has some good data-only deals:
http://prepaid-data-sim-card.wikia.com/wiki/Italy