The Full Form of IMTS is‍ Improved Mobile Telephone Service.

Improved Mobile Telephone System (IMTS) was a radio system that linked to public switched telephone networks (PSTN) before the era of cellular mobiles. It was introduced in 1964 and was the wireless equivalent of landline dial up telephones.

Features

• IMTS was a radio system for mobile telephones that was an improvement over the previous Mobile Telephone System (MTS).

• MTS supported half duplex communication. So, the communicating parties could not communicate simultaneously. IMTS supported full duplex communication, thus allowing both the user to talk and hear simultaneously.

• IMTS required a high power transmitter to be installed, preferably on the top of a hill. The transmitter had two frequencies, one for sending and the other for receiving signals.

• IMTS systems were installed wide apart. The high power requirement in transmitters had the risk of introducing interference in adjacent units. To avoid this, the units were installed far apart from each other.

• It supported only 23 channels. So, users had to wait considerably before getting a dial tone.