I forget what the Italian equivalent of T Com or Vodacom is but one used to be able to buy a sim card from these people with pre paid top up facilities. This enabled one to make comparatively cheap calls from one's mobile.
You can also buy a dongle for use in the computer which is unblocked and so will accept any sim card loaded with a pre paid data bundle. I think that these are illegal in England which is not surprising considering how convenient they are. The simplest and easiest choice of course is to follow the advice already given and stick with your own mobile but with one caveat. I have a feeling that if you call another mobile, as in the UK, from your mobile in Italy, the recipient's mobile gets charged a fee as well. You could perhaps check that with your air time supplier.