Conventional Gear
I think you might have slightly missed my point.
The word 'roger' only means I heard something on the r/t, not that I understood it.
One should not rely on it as confirming that your transmission was understood.
e.g. if you transmit 'G-ABCD radio check' and I reply 'roger', what does that mean?
If I reply 'G-ABCD, receiving you five', then it is rather more meaningful.
Saying I have a spaniel means as little as saying 'roger.' In the case of ready for departure, I cannot do any more than use words that acknowledge your transmission, I'm not allowed to.
I do understand your point about using the A/G service to alert other aircraft to your intentions and it is well made.