Wikipedia defines telegram style, also known as telegraphese, as “a clipped way of writing which abbreviates words and packs information into the smallest possible number of words or characters.” Since telegraph companies charged by the word the style developed to save money while keeping messages coherent.

To me the most interesting part of the Wikipedia article was the examples taken from dictionaries of coded expressions used in telegrams. I was then able to find The A.B.C. Universal Commercial Electric Telegraphic Code (1873) on Archive.org, which helped me understand the point of telegraphese much better. Here are some passages from the preface.

“The Electric Telegraph may be said now to embrace the whole of the civilised world in its network of cables and wires. The largest class of persons who are continually availing themselves of its great and manifold advantages are those engaged in mercantile pursuits. On the other hand, there are great disadvantages connected with the present system of sending messages, not the least important of which are those of expensiveness and publicity. The merchant on looking over his accounts always expects to find the item for ‘telegrams’ a very heavy one; it may, therefore, be assumed, on the ground of economy alone, that he would be found willing to give a fair trial to any good system which guaranteed a considerably reduced expenditure; and there can be no doubt that businessmen generally feel the want of a better and more economical system.”

“Simplicity, Economy, and Secrecy, are the three great objects which the Compiler has kept in view.”

“With regard to Simplicity, every sentence is identified with and represented by a single Code word. This is the simplest and easiest possible method for any telegraphic Code.”

“The Economy of using this Code will be seen at a glance. Very frequently a single Code word represents a complete message, and in other cases a Code word would represent from four or five to upwards of twenty ordinary words. The saving effected on a single foreign message would therefore, in many cases, more than repay the cost of a copy of the volume, and in a short time the saving would be quite a hundredfold. It will, of course, be necessary that any mercantile house using this Code should see that their friends with whom they wish to communicate are supplied with a copy; the cost of which, as before remarked, will be insignificant when compared with the saving effected.”

“The Secrecy of the message between two persons can be made absolute even though any other person may have every command of the telegram and of the contents of the volume. Every sentence is identified with a Code Number of five figures to be found in 1234567890, which can be represented by a group of ten different letters of the alphabet, after the same manner as a tradesman places a private mark on his goods to denote price, &c. All that is necessary is that the two persons shall agree upon any ten different letters that may suggest themselves. Examples will be found on pages vi and vii. It will be seen thereby that the number of possible variations is practically unlimited; consequently, the choice of a Code of ten letters is also unlimited, their great variety admitting of frequent changes if necessary; in fact, the change might be made for every message, or every hour, by agreed arrangement, and thus the absolute secrecy of the Code maintained.”

Following the preface is a detailed example.

“To send a telegram according to the plan of this work first have the message clearly written out at full length, then select the leading words or their equivalents in the message. On referring to the ‘A B C’ the Code Word will be easily found in the next previous column opposite to such leading word or words, for example : —”

MESSAGE.

“There is a favourable change in the market. Telegraph cost, freight, and insurance Petersburg Y.C. Tallow, early delivery, payable one-third on shipment, two-thirds on delivery. We shall be glad to receive your market report. Have you attended to last order? When were the goods forwarded? Present supplies are not equal to requirements. Keep us well advised of sailings from your port.'”

CODED.

“Cementation, Coronet, Hoshama, Depose, Parrot, Gifted, Overmatch, Grayling, Reprisal, Sandy.”

CIPHER.

“With regard to secret telegraphy in cipher, chose any ten different letters of the alphabet, for example ‘March winds,’ to represent 1234567890. As a great number of the sentences are numbered above 9,999 it is necessary to make them all of five figures each; for this reason noughts have been prefixed until the number 10,000 is arrived at. If this plan were not adopted some confusion would arise to the receiver, as the letters would become mixed up. The above message by this plan would be as follows : —
smswd I smcca | msasw | smwwn | scsiw | sahmm | smdw | sahhw | sciis I scdsm
All that the receiver has to do is to tick off the message into groups of five letters each as above.”

The book then contains a 125-page dictionary of sentences, followed by code words for banks, companies, ship’s gear, measures, rates, and more.

If you are interested in comparing different dictionaries of telegraphese, you can check out the 7th edition of The Adams Cable Codex (1894) and others on Archive.org.