Ok, why exactly is this going to the supreme court? It's pretty much a given that if your employer provides a computer, office phone, cell phone, etc., that they can and will monitor its use. The degree of that monitoring maybe vary, but a reasonable person would presume that anything and everything done with work-provided equipment can and will be seen and read.
If you want privacy, use your personal cell-phone. If you want even more privacy, get a pre-paid cell phone (don't feel bad, Tiger didn't thing about that either). Nuff said.