Hi,
You should be able to respond to enquiries through your iPhone. I manage my whole booking mostly through my phone. The AirBnB app gives you the flexibility to be very mobile.
You can also specify from the website (via computer or laptop) if you want to be notified via phone text in addition to the email. This way, I have 3 options to ensure my response rate does not get affected. If there is no internet connection, I can reply via text, it will charge me but I can respond to the enquiry.
The option to respond by email or app requires internet connection.
N