Getting Dollars (Phnom Penh)

Hi all,

I will travel to PP in January and tried already to prepare according to your posts.
One thing is clear, US Dollar will bring you a far way. But how do I get them in PP?

Is it possible to withdraw them at ATMs?
Or somehow else via banks?
Do I have to open an account?

As i will be in PP for Protected content , I do have to get some USD somewhere...

Thanks for your help
Dominik