MTS

MTS stands for Mobile Telephone System.  This is a system that was before Cellular and in fact before IMTS - its more automated counterpart.

One might also think that MTS stands for Manual Telephone System since this system in fact was manual.  To place a telephone call from your car using MTS, you would lift the handset and the unit would transmit and would alert a mobile operator.  The mobile operator would then ask you for the number that you wished to call.  Then the mobile operator would connect you using the frequency channel that you used in order to initiate the call.

MTS systems were common in the US during the early 1970's.  They transmitted on frequencies similar to those used for television - at VHF (150 MHz) and UHF (450 MHz) frequencies.  They were replaced by the more automatic IMTS system in many locations.  Of course, when Cellular became available in the early 1980's, MTS and IMTS systems were in the process of replacement for the more expandable and higher tech cellular mobile telephone products.