CAPT OF A UNITES STATES COAST GUARD HELI ACFT EXPERIENCED DIFFICULTY IN COMMUNICATING WITH TWR DUE TO THE CTLR WORKING SEVERAL POS SIMULTANEOUSLY.

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I WAS THE PIC OF UNITED STATES COAST GUARD ACFT RETURNING FROM OFFSHORE NEAR PASCAGOULA; MS; TO MOBILE REGIONAL ARPT. WE WERE VFR AT 1500 FT; WITH ATIS 22 NM BEARING 210 DEGS FROM MOBILE ARPT (LORAN) WHEN I FIRST CALLED ON 121.0 (SECTOR APCH FREQ). APCH TOLD 'COAST GUARD ACFT CALLING STANDBY' (NO; THIS IS NOT AN ARSA VIOLATION RPT). BY HEARING ONLY 1/2 OF THE XMISSION; I COULD TELL THAT 1 CTLR WAS WORKING BOTH SECTORS. AT 14 NM I CALLED AGAIN AND APCH ACKNOWLEDGED OUR CALL SIGN BUT DID NOT GIVE US A SQUAWK (STILL ON 1200). BY NOW IT WAS CLR THAT HE WAS ALSO WORKING THE TWR POS. AT 8 NM I CALLED AGAIN AND RECEIVED A SQUAWK AND WAS TOLD TO EXPECT TO LAND ON 'A3' (SW SIDE OF RWY 14) VICE THE COAST GUARD PAD ON 'L.' THINGS WERE GETTING BUSY. AT 300 FT AND 1/4 MI FOR A3 I ASKED IF WE WERE CLRED TO LAND ON A3 (RADIOS VERY BUSY). EVENTUALLY WAS CLRED BEHIND AN ACFT ON RWY 14 AND #2 TO THE COAST GUARD PAD BEHIND THE ACFT OFF RWY 18. ALL THE WHILE I WAS STILL UP ON 121.0. THE CTLR WAS WORKING CLRNC DELIVERY; GND; TWR AND BOTH APCH SECTORS. I DON'T HAVE A PROB WITH A CTLR WORKING A COUPLE OF POS. WHAT MADE ME UNCOMFORTABLE WAS NOT BEING UP ON THE APPROPRIATE FREQ FOR THAT PORTION OF AIRSPACE. I BELIEVE I SHOULD HAVE BEEN SWITCHED TO THE TWR FREQ; ALLOWING NO TO HEAR WHAT BOTH SIDES WERE SAYING. IT WAS TOO BUSY FOR 1 CTLR (OR AT LEAST THAT CTLR).