leavingonajetplane:
There is only one 'rule' defining the placement of callsign which is in PANS ATM at 5.2.1.9.2.2 — ''An aircraft station should acknowledge receipt of important air traffic control messages or parts thereof by reading them back and terminating the readback by its radio call sign. (Please note, it states 'should' not 'shall' so it is therefore NOT mandated, and, as yet, ICAO is not fully transposed into law).
Have a look at CAP413 and you will find this:
Continuation of Communications
2.47 The placement of the callsigns of both the aircraft and the ground
station within an established RTF exchange should be as follows:
2.48 Ground to Air: Aircraft callsign – message or reply.
Air to Ground:
1. Initiation of new information/request etc. – Aircraft callsign then
message.
2. Reply – Repeat of pertinent information/readback/acknowledgement
then aircraft callsign.
...which should not come as a surprise seeing as most of us use precisely that procedure.