score:2
I'm not aware of any carrier here that offers the kind of service you need. Most of them have an "unlimited" traffic options but after a certain threshold of GBs what happens is that you can still navigate the web but with a MUCH slower speed.
Your best bet is to subscribe for ADSL and then unsubscribe it before leaving but you have to be VERY careful because you may need to unsubscribe with some kind of forewarning.
The most important carriers in Italy are: