Hello Nowhythisnow!
Thanks for reaching out to the Apple Support Communities. I understand you’re no longer receiving messages from contacts who have an iPhone and are using iMessage. To be sure that we’re on the same page, you have your iPhone settings for Messages > iMessage is turned off > SMS/MMS messaging is on.
If that is correct, your contacts will need to be sure that they have the SMS/MMS messaging turned on, as well as having iMessage on, so they can send message to you through the cellular carrier. This may be an issue which is originating with your contacts iPhone. To be sure, check with them to find out if they are receiving any type of delivery error on their end when they go to send the message to you with both iMessage and SMS/MMS on. If there is no error, try restarting both devices with these steps: Restart your iPhone, iPad, or iPod touch. Try sending again after restarting.
If the message is not delivering and there is no error from the sender, quit Messages and start it again with these steps: How to force an app to close on your iPhone, iPad, or iPod touch. Let us know the results.
Enjoy the day!
