Where is the free software for sending messages to mobile phones from computers?

Sending a text message to everyone on the computer can display the number starting with 16, which only needs to be completed in two steps:

Prepare all the mobile phone numbers in advance, send them to everyone, get them into a spreadsheet, and then pour them into the interface of the required software below.

write what you want the other party's mobile phone to display on the above interface, and it takes 3 seconds to send it all.