International Telecommunication Union. General Secretariat. General telephone statistics compiled from official documents. s.n.
Cita Chicago (17th ed.)International Telecommunication Union. General Secretariat. General Telephone Statistics Compiled from Official Documents. Geneva: s.n.
Cita MLA (9th ed.)International Telecommunication Union. General Secretariat. General Telephone Statistics Compiled from Official Documents. s.n.
Atenció: Aquestes cites poden no estar 100% correctes.