How to write your own software for sending SMS messages?

Question

Python

Hello.
I came up with the idea of ​​writing my own software for sending SMS messages. I would like to know how this area of ​​software development works for these tasks.
Is it possible to write a universal software for sending SMS to all numbers, regardless of the operator (Megafon / Beeline, etc.).
What protocols should be used and how?
If there are tutorials describing the mechanisms of work in this area, I will be grateful for the links.

Answer 1

bfy.tw/ErUG
https://habrahabr.ru/post/256687/
www.sql.ru/forum/660795/otpravka-sms-cherez-grps-modem
tails-up.blogspot.ru/2012/07/sms- gsm-c.html
https://upread.ru/art.php?id=65

Answer 2

If through operators, then they have some kind of API, if through equipment, then this is a serial port and AT commands.