Never mind.
Had my wife download the apk and called her. The call lasted 0:57 and it consumed around 3MB
That's quite a lot for voice only. Was it video too? Or if not, was the audio quality superb?
Lets do some maths for voice only:
1. Assume audio rate is 64kb/s (quite high, but lets be liberal for worst case scenario)
2. So thats 8KB/s, resulting in 480KB after 1 minute.
3. Assuming R2/MB, that would be about R1/min for a call.
Now:
1. You can get away with a bitrate of 32-40kb/s for voice only, resulting in a saving of 25c-50c from the R1/min in (3) above.
2. In (2) above, the 480KB assumes a constant bitrate. But, after a hangouts test yesterday, I noticed that the app detects silence, so it arguably sends nothing in this case. So unless you're a chatterbox, this can also result in savings. May be complicated by the fact that its duplex (x kb/s both ways), so we can discard this for now.
3. (3) above assumes R2/MB. Bundles can greatly reduce the price of a call per minute. Assuming CellC's R15/100meg, (3) above can be reduced to 7,5c/min.
Moral of the story: just like IMs killed off the SMS, these services can kill off voice.