Apps for messaging my phone on my iPad?

First time posting! My husband’s phone has broken. It’s opening day of deer season tomorrow and he HAS to have a way of communicating with me for safety.

If he texts me using iMessage I don’t get notifications because it’s almost like I’m texting myself. (All blue messages on the right side of screen) What app do I download on the iPad so he can text me from my iPad? It has cellular.

I tried WhatsApp but i would need a verification code for his phone number and his phone doesn’t work so I can’t do that.