B737-700 CREW FOUND GND CTL FREQ BLOCKED AND APPARENTLY BEGAN TAXI BEFORE CONTACTING TWR.

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ATC FREQ CONFUSION. PUSHBACK; ENG START; PRE TKOF CHKLIST ACCOMPLISHED NORMALLY. BEGAN ACFT MOVEMENT FROM THE GATE TOWARD TXWY H1. FO TRIED TO CALL FOR TAXI ON 121.8; FREQ BLOCKED. CONTINUING TO MONITOR FREQ FOR SEVERAL MINS WHILE A LENGTHY CLRNC/READBACK WAS BEING ISSUED. I ASKED FO TO CHK FREQ. HE VERIFIED WE WERE ON GND; NOT CLRNC. WE CHKED FOR ALTERNATE GND FREQ. APCHING THE TXWY H1 THROAT WHILE STILL ON THE RAMP; I ASKED THE FO TO TRY TWR ON 118.45. TWR OPERATOR HESITATED; THEN CLRED US TO 'POS AND HOLD RWY 17.' AS WE TURNED ONTO THE RWY HE ASKED US TO VERIFY OUR CALL SIGN AS 'COMPANY NUMBER.' WE REPLIED 'AFFIRMATIVE' AND WE WERE CLRED TO TAKE OFF. DURING CLBOUT; WE WERE INSTRUCTED TO CALL MCO TWR ON ARR IN ZZZ. I CALLED THE MCO CTLR IN ZZZ. HE WANTED TO KNOW WHY WE HAD NOT CONTACTED GND FOR TAXI CLRNC. I EXPLAINED THE CLRNC CONFUSION AND ASKED IF GND/CLRNC WERE COMBINED (NOT ON MCO ATIS). HE REPLIED NEGATIVE; BUT GND FREQ WAS 'CLOBBERED' WITH A FULL CLRNC RERTE AND READBACK FOR CHICAGO FLTS. HE ACKNOWLEDGED THE CONFUSION; SAID 'NO HARM; NO FOUL;' AND ASKED US TO EXPLAIN THAT WE WERE UNABLE TO TALK TO GND WHEN SWITCHING DIRECTLY TO TWR IN THE FUTURE. THE VERY SHORT TAXI DISTANCE FROM THE GATE TO RWY 17; COUPLED WITH THE LENGTHY TIE-UP OF GND FREQ; COMPOUNDS THE CONFUSION. AN ALTERNATE PUBLISHED SECONDARY GND FREQ AT MCO WOULD BE A BIG HELP. NO OTHER ACFT WERE MANEUVERING IN OUR VICINITY OR HOLDING FOR TKOF RWY 17. SUPPLEMENTAL INFO FROM ACN 561977: AFTER COMPLETION ON PRETKOF CHKLIST TO THE LINE; I ATTEMPTED TO CONTACT GND FOR TAXI ON 121.8. FREQ WAS BUSY WITH A FULL CLRNC READBACK. CAPT ASKED IF I WAS ON GND FREQ AND I REPLIED WE WERE. WITH NO OTHER GND FREQS AVAILABLE; I WAS ABOUT TO ASK IF WE SHOULD SWITCH TO TWR (MCO DEPARTING RWY 17; PUSHED GATE) WHEN CAPT TOLD ME TO SWITCH AND CHK IN WITH TWR. AS CAPT HELD SHORT OF TXWY H1; I CALLED TWR ON 118.45 (FREQ FOR RWY 17/35). TWR ACKNOWLEDGED AND TOLD US TO POS AND HOLD ON RWY 17. XING HOLD SHORT LINE; TWR ASKED US TO CONFIRM OUR CALL SIGN AS 'COMPANY NUMBER.' (MY FIRST INDICATION THAT EVERYTHING WAS NOT OK.) AFTER RESPONDING; WE WERE CLRED FOR TKOF. ON DEP; MCO DEP REQUESTED WE CALL TWR WHEN WE GOT TO ZZZ. AFTER LNDG ZZZ; CAPT CALLED TWR WHO SAID THEY WANTED TO KNOW WHY WE DID NOT TALK TO GND. WITH AIRSIDE 2 RAMP NOT CTLED BY GND AND MONITORING GND UP TO TXWY H1 FOR A RWY 17 DEP; I SAW NO PROB AND AGREED WHEN CAPT REQUESTED I CHK IN WITH TWR ON 128.45 AS WE HELD ON TXWY H1.