Mav.... Don't have the direct reference in front of me at the moment, but from memory it is covered in Jepps under the "Transmission Format" heading. As Capt Nomad and NZScion mentioned it is just plain common courtesy not to launch straight into a radio call as the controllers are quite often busy with other things such as co-ordinating hand-offs, datalink exchanges etc. Same deal with OCTA departure and position reports etc.
It also states straight up that
on first contact with ATC one states one's flight rules if IFR. Sounds odd I know, however as usual there are different ways of interpreting the same information contained within the Jepps.
Have a good'n!
OpsN.
