fɹʌm nˈaɪntiːnhˈʌndɹɪd twˈɛnti tˈuː, ðə fˈɜːst θɹˈiː dˈɪdʒɪts əvə sˈɛvəndˈɪdʒɪt səbskɹˈaɪbɚ nˈʌmbɚɹˌɪn ˈʌðɚ wˈɜːdz, ðə lˈoʊkəl ɛkstʃˈeɪndʒ kˈoʊdswɚ ɹˌɛpɹᵻzˈɛntᵻd wɪð lˈɛɾɚz baɪ wˈeɪ əvə nɛmˈɑːnɪk.
From 1922, the first three digits of a seven-digit subscriber numberin other words, the local exchange codeswere represented with letters by way of a mnemonic.