Cambodia – Vietnam

Much the same as getting in. Get a bus to the border, walk then a bus to Ho Chi Minh City.

A explanation of the options and a more important warning about doing this trip can be found on the usualy trip reports.

Buses run a couple of times a day City to City with around 1-2hrs at the border for customs. Total time is 7-10hrs.

A more interesting detour to see the sights would be to catch the ferry from Phnom Penh to Chai Doc (south east).

Phnom Penh 0830 Chai Doc ~1330 or possibly 1200 – 1700 depending on what you look at.

Then a bus to Ho Chi Minh City, possibly the Mailinh Express

This takes around 5hrs.

Allow yourself 2 days to get out.

A side note, Vietnam Railways is funding a study to build a meter guage line from city to city, no details on the route, its part of the Trans Asia Railway, China also has a keen interest in this project.