Visitor location register specification : ETSI technical specification GSM 11.32: release note: version 3.2.1 / European Telecommunications Standards Institute
ETSI TR 102 260 [documento electrónico] : technical report: electromagnetic compatibility and radio spectrum matters (ERM); code division multiple access public access mobile radio (CDMA-PAMR); system reference document / European Telecommunications Standards Institute
Estatísticas dos transportes e comunicações / ed. Instituto Nacional de Estatística
The economist / The Economist Newspaper