Capt Claret is of course correct, but IMHO, I dont think the standard call itself is overly appropriate.
Before descending from controlled into Class G airspace and before separation with any aircraft operating near the base of controlled airspace can be compromised, the PIC of an IFR flight must report position, level, intentions & estimate for next position/destination to the ATS unit providing services in class G airspace
(my bolding). A report is made toATC. As soon as every bug smasher flying around the cotton fields hear 'Centre' they stop listening themselves. A broadcast is NOT required when leaving CTA into OCTA, but alot of people roll the Report and Broadcast into one eg, Centre and All stations Timbucktoo..........