Ok, I seem to recall from back when I was in Vienna (early 90s) the pronunciation zwo statt zwei. I think at the time I assumed it was regional-- some Austrian thing like Zwetschken and Rödeln and Schi-fua–fua-fua-fuan and all that silliness-- but I seem to hear it more and more in recent years. What is the background of this variant and is it becoming more widespead? If so, why?
Thanks!
It’s for clarity. Zwie can sound like something else, but zwo is unique. At least that was my understanding. I picked it up in Frankfurt, fwiw, so it’s certainly not unique to Austria.
Zwo is often used for military marching cadence, presumably because it sounds better for a rhythm.
Oh, I should add, I no longer think it’s Austrian, but is it modern? I know Kraftwerk was using it in the 70s (sorry, embarassing, but that’s my point of comparison for 70s/80s German. . .)
It’s sort of like aircraft controllers saying “niner” for nine.
Is the “o” pronounced in the normal German way, as in Vogel, or is it made to rhyme with the English “two”?
Gestalt
It’s pronounced “zwoh” as in “Vogel”, so no, not like the English “two”.
Like Spectre of Pithecanthropus said, its like saying “niner” for nine in English, it just makes that number sound unique so you don’t confuse it with any of the others.
Here is a recording of a shortwave numbers station where not only Zwo is used, but also Fünnef instead of Fünf, and Zero instead of Null.
I lived in a German city for three years, and in my experience, zwo was almost always used over the telephone when reading out numbers (such as phone numbers and reference numbers). I rarely remembered to use it myself, but no one seemed to mind.
The main reason for the use of Zwo [tsvoː] is that the regular Zwei [tsvaɪ̯] could be confused with Drei [dʀaɪ̯], i.e. three.
Originally if was the female word for two - Martin Luther’s bible translation used (in the nominative case)
zween objects of male grammatical gender
zwo objects of female grammatical gender
zwei objects of neuter grammatical gender
but this distinction has been defunct for centuries - Zwo is used for clarity, irrespective of gender.
In Swiss german , this distinction is still used: (Zürich dialect) zwee Manne (two men), zwoo Fraue (two woman), zwei Chind (two children)
Which is exactly what happened the first time I went to the Beer tent. But the issue of how many beers I wanted was diverted by trying to understand why it was costing so much - €13.
Turns out I was paying a deposit for the glassware. :smack:
And don’t worry, the extra beer got drunk. Well, my wife got drunk cause she had the extra beer 
Si
Interesting. The international phonetic alphabet (alpha, bravo, etc) used in civil aviation actually specifies how numeric digits are to be pronounced. In addition to “niner”, five is to be pronounced “fife”, and always “zero” never “oh”.
The thing that always killed me when Germans would spell at me using phonetics, was “Karl” for K. Even knowing better, my American raised brain always wanted to think C.