Just bumping my old thread to note that the TIM website now formally accepts foreign credit cards. When you go to the homepage or log in, look for Ricarica (as you normally would), and there you'll see a checkbox in the payment details for foreign credit cards (Carta di Credito Estera). Check that and you should be good to go - Visa or Mastercard only for now, per the info note. It'll let you select Amex/Diners, but it won't authorize. I just put 5 euro on both of my SIM cards to keep them active for another year, so I can confirm that it works. You won't see the balance update in real time - it took about 5 minutes on both of my lines.