SIM card for phone in Piazza Navona

Any TIM store. There is one on Via del Corso near Galleria Alberto Sordi.

If you’re flying into FCO, there are two large TIM counters near the exit to terminal 3. To make the transaction easier, you might want to go online and pay for the TIM tourist card and just present your voucher at the counter. The clerk swapped out cards, made sure the new card was activated and it took about 15 minutes. It’ll take about an hour or so before you’ll be able to make calls.