It is important to note that you MUST have a Vietnam visa prior to arrival in Vietnam. Whether by land, sea or air; there is no way to obtain a visa from immigrations in Vietnam. Unless you want to be in limbo waiting for deportation, make sure you get your visa first.
Once you have your Vietnam visa, travel from Phnom Penh to Ho Chi Minh City (Saigon) is simple. Like many places throughout Asia, there are tons of travel agencies to help with all types of travel. We used the Travel agency in our hotel to book onward travel to Saigon. A tuk-tuk arrived to take us to the bus terminal at the scheduled time and the whole trip cost about $6 per person.
As you can see above, the buses from Cambodia were not the newest nor cleanest but they got us to Ho Chi Minh City. The bus company drove to the Cambodian border where we unloaded, obtained our exit stamp and re loaded on the bus. Then we followed the same process on the Vietnam side before reaching our final destination of Ho Chi Minh City. The process was very smooth and there was hardly a wait on either side of the boarder. For those who may be apprehensive about the land routes, don’t worry; they are quite safe and reliable.