Since all editions have different page numbers, it might be best to give you the chapter instead. Leper’s telegram is found at the end of chapter 9. You will find it very quickly. Here are the words. In my edition, it is all in caps.
I HAVE ESCAPED AND NEED YOUR HELP. I AM AT CHRISTMAS
LOCATION. YOU UNDERSTAND. NO NEED TO ASK ADDRESS
HERE. MY SAFETY DEPENDS ON YOU COMING AT ONCE.
(signed) YOUR BEST FRIEND,
ELWIN LEPER LEPELLIER
The caps really do give the feeling of a telegram. This is where Leper becomes a deserter and leaves the military, and, even if the book does not say it, he is likely facing some sort of post-traumatic stress. This point is significant, because Leper is arguably the least likely to go to war. He is a timid, peaceful boy who loves nature. That he goes off to war shows that anyone can go. Also, it shows that the adult world outside can hit any of the school boys in Devon. Thus, Leper reminds the reader that there is war going on in the background, and no one can be immune to it.