Ios9 sends messages, why can't some messages be received?

This is because the default SMS of ios9 is sent via iMessage, that is, via wifi or traffic, similar to QQ or WeChat chat messages; And some friends say that they can't hear from you probably because they don't use iphone, just like you use QQ to send messages to friends on WeChat.

If you want to send it by ordinary SMS, enter the setting information iMessage, turn it off and then turn it on again. You can see that there is an option below to send it as a short message when iMessage is not available. When this option is turned on, you can send it as a short message as long as there is no network.

I just upgraded ios9, and I regret it very much. I still prefer 8.4. I use 5S. I hope it helps you.