| APO | Australian Post Office. |
| APT | Anglo-Portuguese Telephone Company. |
| BPO | British Post Office (the expression used in technical journals). |
| GPO | General Post Office (known internationally as BPO). |
| P&T | Posts & Telegraphs Department (of the Irish Republic). |
| NTC | National Telephone Company (active in the UK until 1912). |
| NZPO | New Zealand Post Office. |
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