Dial the main phone number.
Wait for the automated greeting or dial tone.
Press the extension key format:
If prompted, enter the extension number using the keypad.
If required, press `*` or `#` before or after the extension.
If you reach the wrong person, hang up and try again.
If there is no automated prompt, dial the extension by adding it after the main number when dialing from a phone that supports it (e.g., `main number + extension`).
For some systems, use the format `main number, extension` (pause) by entering the extension after a short pause.