I went to a TIM store in a suburban shopping Mall. The agent spoke English and was very helpful. I asked for the Visitor SIM card and he explained that, a least for me, the better option was a normal prepaid SIM which included 200 minutes of talk, 200 text messages and 500 MG of data for a week. Longer terms with higher limits were also available. He said the Visitor card would be more expensive and provide poorer quality data. So for 5 Reis for the SIM and 5 Reis for the service (less than $3 total) I was set for the week.