[lxgr]

It's definitely not common in Austria, and I also haven't heard it in Germany (outside of a "clarity of communications" context on the phone). Bavarian (which is close to many Austrian German variants) would use "zwoa", which sounds quite different too.

[fnordian_slip]

In Franconia, we use "zwo", "zwä" and "zwei", but it might just be very local to the small towns in my area.

[xen0]

As a non-native speaker, I've used it a couple of times at a bakery to make sure I don't get too much of what I'm asking for.

Doesn't help when I _do_ want three of something though...