If you have noticed to your phone not sending messages or phone calls this morning, that is because there is a nationwide AT&T outage.
One way to fix this issue is to turn on Wi-Fi calling. Go to your settings and search for the tab that says Wi-Fi calling. Once you turn it on you will be prompted to enter your 911 address. After that, it will take a couple of minutes and then it will be activated. You should be able to send and receive messages and phone calls while on Wi-Fi after this.