The most common and most likely answer to this crossword clue is the 8 letter word CHATLINE
I've seen this crossword clue in Independent
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Buddy explains!

The straight part
We know that "telephone service" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case telephone service = chatline.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CHATLINE mean?
CHATLINE noun- A telephone service in which a caller may converse with an operator on a specific subject.
- A similar service which allows conversation among a number of separate callers.