I am not receiving messages from some people. Why?

Grandmaof5sphone- wrote:

How do I know who my cell phone provider is. We don’t have a plan

Well that would be the issue: Assuming you can only receive imessage when you're connected to wifi.

Read here If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support

Grandmaof5sphone- wrote:

How do I receive all messages. I have not been getting half of my text messages and I don’t know why?

contact your cell phone provider, text message is their feature.