In this weekend's Sydney Morning Herald, Lisa Pryor (Eavesdropping on the pot calling the kettle on the mobile black) wrote in a light-hearted way about mobile phone etiquette on public transport but confirmed what we already know (and can't help practising ourselves): public transport is a great place to eavesdrop. Your co-passengers listen to your conversations and sneak looks at what you read.
The same applies to lifts, taxis and planes and any other place you are confined with others.
My concern is the privacy risks that arise from taking business calls or reading business documents in public. The risks include disclosing commercial-in-confidence information (even if it is just the name of the file or the subject of a report you are reading) and disclosing personal information of a customer (even if it is merely the fact they applied for a loan).
There is also a reputation risk: the article mentioned the name of a credit union. It's not clear whether it was a credit union employee discussing his work but it's publicity that may not be positive.
Whilst the etiquette of mobile phones is evolving and there is a huge temptation to answer your mobile phone in public, my opinion is that once you have established the call is for business you should arrange a call back if you cannot move to a private area.