DURING DSCNT FROM FL180; A B757-200 CARGO FLT LOSES ALL VHF COM CAPABILITY AND USES ACARS TO LET COMPANY KNOW OF PROB AS FLT DSNDS INTO AND LANDS AT ONT.

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ON DSCNT THROUGH FL180 ON THE ZIGGY 3 ARR; WITH ZLA; WE SWITCHED FREQS AND TRIED TO 'CHK IN' ON THE NEW FREQ NUMEROUS TIMES UNSUCCESSFULLY AND RETURNED TO OUR PREVIOUS FREQ. WE WERE CLRED TO CROSS DAWNA INTXN AT 12000 FT (AS PUBLISHED) AND GIVEN A NEW FREQ TO TRY FOR ZLA. AGAIN; WE TRIED NUMEROUS TIMES TO ESTABLISH CONTACT ON THE NEW FREQ; TO NO AVAIL. PRIOR TO AND AFTER DAWNA; WE COULD NOT CONFIRM IF WE WERE XMITTING OR RECEIVING. WE TRIED ALL MIKES ON ALL COM RADIOS. WE ATTEMPTED TO RAISE ANYONE ON ZLA; ONT TWR; AND SOCAL'S CHARTED FREQ. WE MONITORED ALL COM AND NAV RADIOS; SPECIFICALLY THE ILS FREQ TO RWY 26L AND PDZ VOR (112.2). WE SENT A MESSAGE TO THE COMPANY VIA ACARS TO THE EFFECT THAT 'WE HAD LOST ALL COMS WITH ATC.' WE CHKED THAT ALL CIRCUIT BREAKERS WERE 'IN.' WE MADE OUR XING RESTR AT DAWNA AS CLRED. WE WERE TROUBLESHOOTING THE PROB AND WERE ATTEMPTING EVERYTHING TO RE-ESTABLISH COMS BEFORE DSNDING FOR THE APCH. WE SLOWED THE ACFT DOWN TO GAIN MORE TIME. AT THE POINT WHERE WE DETERMINED THERE WAS NO WAY TO RE-ESTABLISH COMS; WE WERE XING PETIS AND WERE STILL AT APPROX 10000 FT (4200 FT IS NORMAL XING ALT). BECAUSE OF SEVERAL FACTORS; WE OPTED TO MAKE A R 360 DEG TURN TO LOSE ALT; RUN CHKLISTS; RE-ENTER THE APCH IN THE FMC AND GET US IN A SAFE POS TO FLY THE ILS APCH TO RWY 26L. AMONG THESE FACTORS WERE LAX CLASS B AIRSPACE BEYOND ONT; MOUNTAINS TO THE R AND BEHIND US; AND FUEL WAS BECOMING LOW (LANDED WITH 7800 LBS). FORTUNATELY; THE WX AT THE TIME WAS VFR AND WE WERE ABLE TO CLR THE TURN BY MONITORING FOR TFC VISUALLY. ONT TWR HAD CLRED THE AIRSPACE FOR OUR APCH; AS WE WERE LATER INFORMED. WE RECEIVED AN ACARS MESSAGE RESPONSE FROM THE COMPANY AFTER CAPTURING THE LOC ON THE APCH. ALL THE AFOREMENTIONED REASONS CREATED A BUSY WORKLOAD FOR THE FLT CREW. ITEMS WERE PRIORITIZED AND NON ESSENTIAL TASKS WERE COMPLETED AS TIME PERMITTED. WE LANDED UNEVENTFULLY AND CLRED THE RWY. WE STOPPED AND WAITED FOR LIGHT GUN SIGNALS BEFORE PROCEEDING WITH OUR TAXI TO OUR RAMP FOR PARKING.