International flights arrive at Ho Chi Minh City (SGN) or Hanoi (HAN) airport. From there you need to catch a domestic flight to Phu Cat (UIH) airport near Quy Nhon. Domestic flights are frequent and cheap; Vietnam Airlines is usually very reliable.
If you need to stay overnight near the Ho Chi Minh City airport, IBIS Saigon Airport Hotel is a good option since it is in walking distance.
We will provide transportation from UIH airport to your hotel in Quy Nhon.
You can read a description how to travel to Quy Nhon through Ho Chi Minh City airport here