A B757 FLC CONTINUED TO TAXI WITHOUT A CLRNC AFTER THEY WERE UNABLE TO CONTACT GND CTL ON THE ASSIGNED FREQ. ALLEGEDLY; THE B757'S MOVEMENT WITHOUT A CLRNC CAUSED ANOTHER ACFT TO BRAKE HARD. AFTER THE CREW ARRIVED AT THE RAMP; THEY WERE TOLD TO CONTACT THE ATCT GND CTLR ON ANOTHER FREQ WHO QUESTIONED THEIR TAXIING WITHOUT A CLRNC.

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AFTER CLRING RWY 12 AT MIA; WE WERE INSTRUCTED TO CONTACT GND CTL ON 121.8; WHICH WE TRIED TO DO UNSUCCESSFULLY. SINCE WE CLRED AT TXWY V AND WERE ENTERING THE RAMP AT 7; AND SINCE RAMP HAD ALREADY CLRED US INTO THE RAMP; WE SWITCHED TO RAMP FREQ AND ENTERED THE RAMP RATHER THAN BLOCK ANY POSSIBLE TFC BEHIND US. AT THE TIME THERE WAS NO TFC ON EITHER THE INNER OR THE OUTER TXWY AND THERE WAS TFC CLRING AT TXWY V BEHIND US. UPON ENTERING THE RAMP; RAMP SAID TO CONTACT GND ON 127.5. WE DID; AND THEY GAVE US A LECTURE ON TAXIING THE 50 YARDS OR SO; WITHOUT CLRNC FROM THEM. SUPPLEMENTAL INFO FROM ACN 329730: I TWICE ATTEMPTED CONTACT WITH MIAMI GND ON 121.8 WITH NO SUCCESS. THE FREQ WAS CONGESTED. AFTER WAITING FOR TFC TO CLR THE ALLEY WE WERE CLRED BY RAMP CTL TO TAXI TO THE GATE AND WERE TOLD THAT GND CTL ON 127.5 WANTED A CALL. I CONTACTED GND CTL AND WAS INFORMED THAT WE HAD BEEN BLOCKING TFC AND REQUIRED A CLRNC TO TAXI ON THE ARPT. APPARENTLY WE WERE ASSIGNED THE WRONG GND CTL FREQ FROM MIAMI TWR. THIS WAS NOT APPARENT AS WE CLRED RWY 12 SINCE 121.8 WAS CONGESTED AND WE RECEIVED NO REPLY. SUPPLEMENTAL INFO FROM ACN 329721: ACFT #1 TAXIED TO THE RAMP WITHOUT CLRNC. ACFT #2 HAD TO HIT BRAKES HARD TO STOP.