jpaik, as mentioned you definitely should not buy a full price iPhone from the carrier - get it from Apple instead. But if you do get a phone from your carrier (whether it be a subsidized iPhone or some other smartphone), look online for an unlocking service before your trip to Italy. For example, most Android phones can be unlocked for less than $20 online.
I have an unlocked Nexus One and was recently in the UK. Upon arriving at LHR, just went to the Vodafone store in the terminal and got a dirt cheap pay as you go SIM. So before I even walked out of the terminal, I was up and running with a phone number, text messages, and full internet on my own phone (not some cheapo crap dumb phone). Since it was my own smartphone I had Google maps, GPS access, full web browsing etc - things you won't get from an off the shelf pay as you go phone from them.
The only thing is that you might want to look up the pay as you go APN settings for the Italian carrier before hand and know how to punch that into your phone when you get there.