Brazil is a dual band CDMA/GSM country. So pretty much any CDMA VZW phone will be able to work down there for calls. Data services will require a GSM capable device.
What kind of Blackberry do you have?
What city in Brazil are you in?
Did you dial *228 back in the United States before leaving?
If you have a GSM/CDMA Blackberry (Storm 1/2, 8830 or Tour) check your mobile network options. Click on Options > Mobile Network and make sure Network Technology is set to Global and the Network Selection Mode is Automatic.
If you're able to call from your cell phone or another line you can dial: 908-559-4899 to reach Global Technical Support. They're open 24/7 to help troubleshoot your phone.
Also keep in mind that international service can not be guaranteed by any means. VZW does not own or operate the network in Brazil and rely on the local telecomm carrier to support your device. In some parts of the world cellular networks aren't as good as VZW's back here in the states.
Best of luck to you.
I did everything you suggested when i was in a small town but it didn't work. Now that I am in Sao Paulo I figured it should find a signal automatically. I even tried searching for connection manually but it didn't work. The only thing I didn't do was choose "Global." It works! Thanks for your help.