The Clue No. after a telephone no.
The Answer EXT
The clue "No. after a telephone no." refers to a common abbreviation used in phone numbers. "EXT" stands for "extension," which is often added after the main telephone number to reach a specific person or department. When dialing a phone number, you might see "123-456-7890 EXT 123," where "123" is the extension. This makes "EXT" the perfect answer to the clue.