I've certainly done this enough times myself, normally with a landline phone while talking someone else through some complicated operation where I need both hands free. I wouldn't want to do it for a prolonged period of time, but it's much less awkward than trying to type or dismantle something with one hand...

When this picture first started making the office rounds in the 1990s it was the "laugh of the day", eliciting chuckles from many a cubicle. For some reason today it doesn't seem as funny. Probably because when this picture first came out, the idea of a hands-free cell-phone was a novel idea (notice the old mid-90's clunker phone), hands free cell phones were not available at any price, or only just becoming so - this was almost certainly an office joke from the mid-90's on how to have "affordable" hands free. Today it just seems like a vision of third world cleverness and has lost its historical context, what is old seems new again.

I don't know whether it's authentic or not, but it was featured on every gadget blog several years ago, usually under the headline "Look Ma, no hands!".

Another joke?, this looks like someone commercialized the concept.

And related, another another (resourceful) way to wear your cell phone

It originates from South Africa, the poster at the back is from South Africa's power distributor.