MD80S ON APCH VECTORS. CALL SIGN SIMILAR WITH ANOTHER ACFT ON SAME FREQ. CTLR GOT 2 ACFT MIXED UP AND SWITCHED RWY ASSIGNMENTS SEVERAL TIMES.

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AT APPROX XA35L WE WERE TOLD TO EXPECT ILS VECTORS FOR ILS RWY 17R. WHILE BEING VECTORED THE APCH WAS CHANGED TO ILS RWY 18L. SHORTLY THEREAFTER; WE WERE TOLD TO MAINTAIN 4000 FT AND VECTORED SE. A NEW ATC FREQ WAS ASSIGNED AFTER RADIO CONTACT WAS ESTABLISHED. WE WERE TOLD TO EXPECT VECTORS BACK AROUND FOR ILS RWY 17R. AT 15 NM ESTABLISHED ON THE APCH WE WERE TOLD TO CONTACT TWR ON 126.55. AT 13 NM CONTACT WAS ESTABLISHED AND WE WERE CLRED TO LAND ON RWY 18L. I THEN ASKED FOR VERIFICATION OF THE LNDG RWY. THE CTLR CORRECTED HIMSELF AND STATED THAT WE WERE CLRED FOR LNDG ON RWY 17R. WHEN I QUESTIONED HIM TO THE AMOUNT OF CONFUSION; HE STATED THAT FLT XX HAD CUT ACROSS OUR INTENDED APCH COURSE RESULTING IN OUR APCH CHANGES AND ADDITIONAL VECTORS. POSSIBLY THE SIMILAR CALL SIGNS RESULTED OR ADDED TO THE CONFUSION. CONSIDERING PRIOR APCH CTL INSTRUCTIONS THERE WAS A LOSS OF CONFIDENCE IN THE COCKPIT WHEN TWR CLRED US TO LAND ON THE W SIDE WHILE ON ILS FINAL FOR RWY 17R. I SUGGEST SIMILAR CALL SIGNS BE ELIMINATED ASAP.