GOLD doesn´t establish what´s first, voice or CPDLC. Pargf. 5.1.3.1 says crews should normally chose CPDLC as mean of communication and leave voice as back up. And later appeals to crew to determine which communication medium to use (unless otherwise stated).
It refers you then to ICAO 4444 pargf 8.3.2 that stablishes voice before any surveillence service ,(CPDLC included) quite complementing with Willise´s post.