Arriving by plane

Hi there,

I was wondering if you could help me  urgently. My partner was supposed to sort out our Visa's but he hasn't  (of course I did not find this out till too late..) but I heard we could only get Visa's on arrival if we flew into Vietnam. But we will  actually be in Cambodia prior to Vietnam. if we fly from Cambodia to  Vietnam, does this count?

Hope to hear from you soon