The Brazilian mobile phone infraestructure is complex. There isn’t a single company operating on the whole of the territory. Each state has a number of companies active on that state. Some companies can be found in several states, others can’t (Telemig, for instance, is a company active only in the state of Minas Gerais). To complicate things even more, some companies work with GSM technology, others with TDMA o CDMA.
Careful with mobile phone cloning. It’s a common occurrence in Brazil.