Quick question over DVD regions

I'm usually based in Australia, and am staying in the US for a few months.

I usually purchase RT DVDs on there store, and often don't worry about Region-Locking. But I am making an Amazon purchase, and want to add some RT DVDs to the order.

If I purchase the DVDs from Amazon, will they have the DVD Region locking, or will they be supported on Region 4 DVD devices?