For coverage check here:
Wind - Privati - Copertura Rete Mobile
TIM
P.S. I regularly use voip on internet no stop. It's not allowed only officially.
If you choose TIM remember:
40 hours are billed in 15 min session, so if you connect for only one minute you'll be charged of 15.
When you finish your 40 hours bundle you pay (i don't know how much)