Before STD (Subscriber Trunk Dialling) codes were introduced in Northern Ireland, during the 1960s and 1970s, an operator based system was in operation. Each subscriber had short (usually 3 or 4 digit) number within the local exchange. For example, the post office in Dromore was Dromore 201 .
Subscriber Trunk Dialling
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Subscriber Trunk Dialling - Exchange Code - England Phones
Subscriber Trunk Dialling - Exchange Code - England Phones
Subscriber Trunk Dialling England
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