The key here is making sure that your phone has the ability to surf the internet using the GPRS or EDGE standards - not all GSM phones do.

If your phone has that feature, you will need either a USB cable or bluetooth receiver for your notebook to use the phone as a modem (I would test/install this before leaving if possible). You then connect just like you would with a wired (LAN) or WiFi connection, no provider to dial up.

It's quite affordable to use GPRS/EDGE in Italy with a locally bought SIM card - TIM for example offers 500 MB for EUR 20, and if you purchase another 500 within 30 days, they throw in another 500 for free, so 1'500 MB for EUR 40.
http://www.privati.tim.it/pr/pr_dett...7_6979,00.html

Alternatively, EUR 25 will get you almost unlimited e-mail access (9 GB) on evenings and weekends for 30 days. This somehow also cheapens regular access during business hours which costs 6.14 EUR per MB otherwise - but claiming that bonus looks quite complicated.
http://www.privati.tim.it/pr/pr_dett...7_6950,00.html

Both deals are good until July 2nd 2006, but could be extended. Assume the other carriers offer similar deals.

Hope this helps,
Andre