STD Full Form
The full form of STD is Subscriber Trunk Dialing. This technology allows subscribers to make trunk calls directly without relying on telephone switchboards. This term is used in Australia, India, Ireland and the United Kingdom. Kanpur and Lucknow were the first cities in India to have STD service introduced in 1960.
ISD Full Form
The full form of ISD is International Subscriber Dialing. ISDs are used for international calls that are dialed directly by subscribers. The United Kingdom was the first to use this term. To make an international call, first dial the international dial-out code of the originating country, then dial the country dial-in code of the destination country, and finally dial the destination number.
PCO Full Form
The full form of PCO is Public Call Office. It is a publicly accessible coin-operated telephone system in India and Pakistan. According to TRAI, India has more than 40 lakh (4 million) PCOs installed, with Bharat Sanchar Nigam Limited (BSNL) being the country’s largest PCO operator.