I traveled all over Italy using TIM and had no issues with connections/service. I had been to Capri, Milan, Verona, Roma, Salerno, Casal Velino, Ascea etc.. etc..
I also use their TIMxSMARTPHONE service for 3G which came in handy for $2.50/week. You can setup Skype and call internationally for very cheap. Or use Skype/Skype for free. I'm not sure of the costs with TIM's international calling plan though.
The only thing that concerned me was that this past week, they took $6.70 out of my account with plans that cost $4.50/week. No one at TIM had any idea either.
Other than that, I recommend them.