Its not that difficult but you need to be clear on which boxes you are ticking.
Below is a summary of some of the procedures (i really can't be bothered citing all the authorities).
On first contact with all CPDLC facilities, (on either VHF or HF), the CPDLC
suffix must be added to the flight callsign e.g. Montreal Centre Barnburner123
If entering another Oceanic CTA/FIR this must be stated:
e.g. Gander Radio,Barnburner123 CPDLC, Shanwick next, SELCAL ABDC.
Iceland - If the next CTA/FIR is domestic airspace, the NAT exit point/domestic entry point must be stated:
e.g. Iceland Radio, Barnburner123, CPDLC, exit DARUB.
Take a look at ICAO NAT Doc 007
Last edited by cribble; 19th Dec 2012 at 08:52.