I have worked with sms clients in linux paltforms for more of 6 years. If you need a software to send message using SMPP protocol (send sms to the mobile operator) i can set up one for you fast in a linux platform, or in a docker container if you prefer to move it to any kind of server.
I would recomend use an existing software (FREEWARE), it has already solved a lot of issues to sending sms.