Tips to know about telephoning in English
1. we say phone number digit. Two consecutive number the same are usually spoken as “double…”. Three consecutive number 222 the same can be spoken as “triple two” or “two, double two”.
2. Telephone number should be grouped to make them easier to remember. International, national and local code should be followed by a pause. Subscriber numbers should be split up into smaller groups of three or four numbers.
3. “O” is pronounced “oh” in British English, and “zero” in American English.
4. Extension number is an internal (office) number.