I'm Apple 5s from Telecom. How to send free text messages with Apple?

First of all, thank you for your telecom support.

According to your description, sending free SMS between Apple 5s and Apple requires that both Apple phones are set with IMassage.

Specific settings:

Settings → Message Hook Imessage

Press the prompt setting function to publish Imessage blue directly.

If you need to audit and pay, please go to the business hall of Anhui Telecom Network. Have a nice day.

I hope my answer to your help can be adopted by you!