The privacy rights of public employees in text messages they send and receive on mobile phones provided them by their public or government employer came before the Supreme Court on Monday in the case City of Ontario v. Quon.  The employee, Jeffrey Quon, a police officer was fired after his supervisor read sexually explicit text messages sent to and from his girlfriend on a mobile phone that had been provided to him by the police department. Interestingly, Quon was told that he could use the device on his own time if he paid the extra cost. 

Quon's situation is different from private company or corporation employees because he is a public or government employee. Public employees have some constitutional protections in this case the prohibition of the Fourth Amendment on unreasonable search and seizures, i.e., the reading of his private text messages. Private company employees almost without exception have no constitutional protections in their job.

You can read more about City of Ontario v. Quon in the Los Angeles Times, "Justices hear case of Ontario police officer who sent risque messages."