@Huma0 You're right, I don't think it matters whether it's an iphone or an Android, Airbnb seems to think everyone goes out and buys a new phone every year and if you don't, too bad for you.
@Carl-and-Sally0 You can still use your phone to answer messages without using the app. I have never used the app.
Just log on to Airbnb on your phone using the browser, not the app. You'll get the desktop site. It doesn't appear on your phone exactly the way it does on your laptop, it's a bit harder to navigate, but I have easily been able to answer messages in my inbox that way.
Just because various websites offer an app doesn't mean you have to use it. Almost any website can be accessed on a smart phone through the browser.