Presidential communications are logged and filed, so that there is a record of who called who when. In some cases a synopsis is filed too.
Remember in the Vince Foster hubub, it was found that there were three or four mysterious lines installed that went around the White House switchboard? It was fixed right away but was immediately recognized as an accountability problem (I think Hillary took credit for the lines).
So THIS president fussed and held his breath until he was allowed to keep an off-the-record personal communications device with no accountability, oversight, or transparency.
I wonder if the inevitable court challenge will succeed?