Hey...
A couple of items based on my own cell phone "experience" here. If you buy a chip here you will most likely have to have the bill of sale for the phone you want to use, or they won't sell you a chip. If you get a "pre-pago" chip you will not be able to use the phone internationally. If it all gets too complicated and you want to buy a cheap phone and service down here, you won't be able to as you do not have a CPF (Brazilian SSN).
All this is because done to combat cell phone theft. Depending on what you intend to use the phone for (personal security, infrequent home contact, heavy business usuage, etc.), you might want to consider getting international service with a US carrier, and being carefulo with the usage. I have a North American phone as well as a Brazilian one (after working thru my "experience"). The NA phone is about $2.00US for each connection plus $1.00/minute. I think TIM is the best of the Brazilian providers.
Boa sorte...