The most common and most likely answer to this crossword clue is the 6 letter word LOWING
I've seen this crossword clue in The Sunday Telegraph
L
O
W
I
N
G
More clues leading to the result LOWING
Buddy explains!
The straight part
We know that "calling from Jersey or Guernsey" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calling from jersey or guernsey = lowing.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 LOWING mean?
LOWING verb- To depress; to lower.
- To moo.
- To burn; to blaze.
- The sound of something that lows.