i got such a sim when i was there once..it was exceedingly difficult as i dont speak portuguese. they were very helpful but when i finally got the thing up and running it was regionally limited..i could only ring between sao paulo and rio and one other city which ive forgotten.
nowadays i have a skype number and people ring me on that and i collect my voicemail from skype a couple of times a day and return the call on skype. internet cafes are common in brazil and people are entirely accustomed to people wearing headphone/mics sitting and making calls