Sorry, my fault, now the page is updaed:
http://www.prepaidgsm.net/en/italia/h3g.html
I added some info on the Skypephone too...
BTW, basically the Skypephone works quite differently than programs like Fring on a Nokia Series 60. You are not using VoIP on the UMTS network (with often very low quality and long delays), but it's a normal (toll free) call to a special number which forwards your call through VoIP to the other Skype user. So quality is really not bad (even of course a bit lower than a normal phone-phone call).
With 3 you have a very good option for mobile internet which is called "Naviga 3": it costs € 9/month and you get 50MB of data every day.
There's plenty of shops in Florence, take a look
HERE. You can also ask help to my "colleague" AndreA, he's from Florence.
The Skypephone is a ZTE, so Chinese phone, but it shouldn't be bad...