Mobile telephony
MTD (Swedish abbreviation for "Mobiltelefonisystem D", or "Mobile telephony system D") was a manual mobile phone system for the 450 MHz frequency band. It was introduced in 1971 in Sweden, and lasted until 1987, when it was made obsolete by the NMT automatic service. The MTD network had 20,000 users at its peak, with 700 people employed as phone operators.