Edit: No surprises in the SA Supreme Court decision of Savage v Police  SASC 13, reported as though it was news here. The decision was more about a magistrate's discretion to award a conviction. The issue of merely using a phone to check the time was dismissed immediately, with reference to Kyriakopoulos v Police  SASC 71.
When the Road Rules 2009 came in the rule-makers had significantly changed the rules about using a mobile phone when driving. Rule 300 became much longer and more detailed. It was clearly the intention to make use of a hands-free kit legal, while almost any other use of a phone while driving remained an offence.
News reports this week carry Monash University Accident Research Centre findings that hands-free isn't that much safer than hand-held mobile phone use. The Draft National Road Safety Strategy for 2011 - 2020 reportedly floated a total ban on mobile phone use behind the wheel, but it's already been ruled out.
There's nothing new in this information. A MUARC report from 2003 reviewed the available literature and identified a number of studies that found hands-free phones were not, or were only a little, less distracting than actually holding the phone. Programming a sat-nav system was found to be one of the most distracting tasks a driver could perform. One study quoted eating and drinking as being more statistically dangerous than using a mobile phone.
This raises the question of whether a driver could be prosecuted for inattention when using a hands-free mobile phone (for example, where they have an accident). Rule 300(1) offers a defence to the offence created under rule 300, but not to offences under rule 297 (driving a vehicle without proper control) or under s 65 (careless driving) of the Road Safety Act 1986. (Or, to pick the most extreme example, culpable driving under s 318 of the Crimes Act 1958).
It could be argued that legislators have created a misleading impression of safety by making hands-free use specifically legal, where the previous law was unclear. But is this like claiming its okay to speed because of the 10% leeway permitted for speedometers in the standards for roadworthiness? (The argument swiftly dismissed by the SA Supreme Court in Police v Van Reesma  SASC 201.)