Vietnam has good domestic flight connections, with new routes opening up all the time, and very affordable prices (if you book early). Airlines accept bookings on international credit or debit cards. It’s safest not to rely on a flight from a regional airport to make an international connection the same day – travel a day early if you can. Vietnam Airlines also flies domestically.
It’s hard to get reservations for flights to/from Vietnam during holidays, especially Tet, which falls between late January and mid-February.
There are four established international airports in Vietnam. Others including Phu Quoc and Hue are officially classified as ‘international’ but at the time of research had no overseas connections (apart from the odd charter).