Complex sentence: An Airfone telephone is usually located in the seatback of the seat in front of the passenger, there may only be one per row in coach class, while first class may have one per seat.
Split into simpler sentences: An Airfone telephone was usually located in the seatback of the seat in front of the passenger. There may have been only be one per row in coach class, while first class may have had one per seat.