OK, no reply to my comments
Anyhow I'll share the result in case it's useful to someone else.
I finally got to talk to TIM.
The 2Euros was because I was navigating with the APN wap.tim.it
The operator told me, "Mai usar wap". Never use wap else you'll be charged 2 Euros per day.
The other problem remains. With the APN set to wap.tim.it, I cannot tether my iPhone to the PC. So I've left it at that for now. Seems to be a problem restricted to iPhone 4s only
