Ok, I got my unlocked, tri-band (850/1800/1900), GSM phone ready to take to SP and to Rio. I've read here about buying calling cards, buying phones locally, renting phones and guides/landlords offering sims to their clients/tenants.

But I haven't found info on where to buy a sim card to use in my phone? I will be staying in a hotel. Any suggestions? Are they easy to find? Any estimate on the cost?

My understanding is that with a sim card and another card with service credits that are purchased locally, I will have a temporary local number that I can use with my current phone to place and receive calls. Am I correct?

I also read that the phone companies are different between SP and Rio. Does this mean I need to get a sim and service card in each place if I want to use it in both cities?

In Sao Paulo look for the TIM sign. There are many TIM dealers where you can purchase a SIM card. The SIM card itself is R$25 and you then buy time cards with the time, which runs a bit over R$1 per minute for local calls.

You will then have a local number. I am quite certain the SP number will place and receive calls to/from Rio, although the per minute charge may be slightly higher to reflect that it is technically long distance.

Your hotel will be able to direct to you a TIM store.