B727 CREW DID NOT OBTAIN CLRNC TO ENTER THE RAMP AREA FROM RAMP CTL.

Narrative

THE CAPT STOPPED THE ACFT ON TXWY K SHORT OF INTXN E; WAITING FOR THE SO TO TALK TO RAMP CTL ON 129.55 FOR ENTRY INTO THE RAMP AREA. THE SO WAS TALKING TO COMPANY OPS AND CONFIRMED THE GATE ASSIGNMENT AND TOLD US THAT THE GATE WAS CONFIRMED AND WE TOOK THIS TO MEAN THAT HE HAD ALREADY TALKED TO RAMP CTL. AFTER ARRIVING AT THE GATE; WE WERE ADVISED BY MESSAGE FROM OUR COMPANY OPS THAT WE HAD FAILED TO CONTACT THEM FOR CLRNC INTO THE RAMP AREA. THE SO RESPONDED THAT HE HAD ONLY TALKED TO COMPANY. ON 3 PERSON COCKPITS OUR SOP IS THAT THE FO TALKS TO GND/TWR; ATC; ETC; AND THAT THE SO TALKS WITH RAMP CTL AND COMPANY OPS FOR RAMP TAXI GATE ASSIGNMENT; ETC. THE CAPT AND I WERE AWARE OF THE NEED TO CONTACT RAMP FOR CLRNC AND MISTOOK THE SO'S INSTRUCTION/RESPONSE TO MEAN WE WERE CLRED IN. THIS DIVISION OF COMS OFTEN CREATES CONFUSION BECAUSE THE 2 PLTS UP FRONT ARE 'OUT OF THE LOOP' DURING A BUSY PERIOD (CLRING RWY; TALKING TO GND CTL; AFTER LNDG FLOWS) AND IN OUR HASTE TO START INTO THE GATE AREA; PROCEEDED WITHOUT PROPER CLRNC IN DUE TO COMS BREAKDOWN IN THE COCKPIT. I FEEL THAT THE FO PNF SHOULD MAKE ALL CALLS TO RAMP; GND TWR ON 3-MAN COCKPITS JUST LIKE 2-MAN COCKPITS. THIS WOULD RAISE THE WORKLOAD FOR FO BUT WOULD GREATLY INCREASE THE OVERALL SITUATIONAL AWARENESS OF THE CAPT/FO.