I gotta find that gas station! I'm...

I gotta find that gas station! I'm planning a trip to Vietnam for about a month and a half from now, lasting for about two weeks. I keep getting iffy info about communication though so i have a question: are you using a cell phone for communication and if so did you have to get it there? I'm trying to find a universal way of getting in touch with people because right after I'm going to Australia and i dont want to have to buy new stuff for that, telephone wise lol any advice?

Heading South?