@Kurtis19 I do not rely on replying or doing anything with my iphone and the AirBnB App. As a host, there are too many pitfalls. You may want to look at Using Scheduled Messages in the Resource Center.
Unless you are going to be away from your computer for too long, i.e., more than 12 hours, wait until you are logged in to take care of business. I know that there are many hosts out there that don't have issues with their phones and the App -- I happen to not find it as reliable as working from my computer.
@Kurtis19 I have the app, and find it's the best for ease of communication. I get an immediate notification of a message or booking, and can go right to it. From an email notification, I hit reply and get taken straight to the message in the app.