CL65 CREW ON A VECTOR TO TLH FOR AN ILS TO RWY 27 CIRCLE TO RWY 18 ARE SWITCHED TO THE WRONG FREQ FOR TURN ON TO LOC.

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ENRTE TO SZW VOR DSNDING TO 11000 FT; WE RECEIVED THE INSTRUCTION TO 'TURN L HEADING 160 DEGS; DSND AND MAINTAIN 7000 FT; VECTORS FOR THE ILS RWY 27 AT TLH.' I INITIATED THE TURN AS THE FO ASKED IF THE ALT WAS 7000 FT. I REPLIED 7000 FT BUT PER THE COMPANY PROCS WHEN A DISCREPANCY OCCURS; I HAD HIM VERIFY THE ALT. WE WERE TOLD TO 'TURN L HEADING 160 DEGS; DSND AND MAINTAIN 8000 FT.' THEN WE WERE TOLD TO CONTACT TLH APCH. WE RECEIVED A CLRNC TO 5000 FT. APCHING THE LOC COURSE AND NOT ON AN INTERCEPT HEADING; I HAD THE FO ASK APCH FOR A TURN. THEIR ACKNOWLEDGEMENT WAS 'WHO?' AS IF THEY HAD HAD NO EXCHANGE WITH US. THEN WE BELIEVE WE WERE TOLD TO CONTACT TLH APCH ON ANOTHER FREQ. THE RESPONSE WAS 'WE HAVE BEEN TRYING TO CONTACT YOU FOR THE LAST 20-30 MI.' WE WERE THEN GIVEN VECTORS TO REJOIN THE LOC AND MADE AN UNEVENTFUL LNDG. DISCUSSING THE SIT WITH THE FO AFTERWARDS; WE TRIED TO RECOLLECT THE SEQUENCE OF EVENTS AND DETERMINE WHERE AND WHEN THE ERROR WAS MADE. HE AND I WERE IN FIRM AGREEMENT THAT THE ERROR HAD TO BE ON THE PART OF THE CTLR. WE CONSIDERED THE SIT TO WHERE WE MAY NOT HAVE SELECTED THE XFER SWITCH BUT NEITHER OF US HAD TOUCHED THE AUDIO PANEL SINCE THE INITIAL CONTACT WITH APCH CTL. ALSO; THE FO HAD PRE-SELECTED THE TWR FREQ IN THE STANDBY BOX. I TELEPHONED APCH CTL ONCE ON THE GND. HE MENTIONED THAT THEY WERE TRAINING A NEW CTLR. HOWEVER; NEITHER OF US WAS CERTAIN WHERE AN ERROR OCCURRED.