Go easy on me
Ive been retired from flt ops for a decade or two but I do remember at the end of the ATC fpln entering REG and SEL.
If we needed to contact an a/c we would phone stokholm radio or portishead radio and im sure i gave the selcal and approx position so when contacted they would be patched through via landline.
So we didnt bother ATC with this communication