First off, let me assure you that the lack of Portuguese language prompts is purely coincidental and not out of spite or prejudice. You may look around and find that prompts for your language are very limited for other systems too, infact looking around the vast spaces of the internet I was only available to find one free set of language prompts for Portuguese. Even Astrix, the hugely popular open source has pointed people to a third party company for prompts.
Check this out;
http://sourceforge.net/projects/disc-os/files/Disc-OS%20Sounds/1.0-RELEASE/Disc-OS-Sounds-1.0-pt_BR.tar.gz/download
Create a new prompt set in 3CX, and Viola, Your all set.
There is a program out there called audacity that can assit you in editing the audio files accordingly.