Inspired by this post in TIL, the linked article mentions that
Telegrams reached their peak popularity in the 1920s and 1930s when it was cheaper to send a telegram than to place a long-distance telephone call.
So how expensive was sending a telegram at that time in today's money? And how about a long-distance phone call?
An important thing to note was that there were multiple telegram networks, a city wide 10 word telegram might cost 20 cents by the 1920s (and a large amount of that may be hand to hand delivery) while a city to city might cost 60 cents.
Hope that gives you some information.