MD88 FLT CREW ACKNOWLEDGED DSND CLRNC MEANT FOR ANOTHER SIMILAR SOUNDING ACR; BUT UNCHALLENGED BY ZAU.

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WHILE OPERATING ACR FLT #AABC ON THE EAU CLAIRE ARR (EAU.EAU6) INTO MSP; WE RECEIVED A CLRNC TO DSND TO FL240 FROM ZAU. THE CLRNC WAS ACKNOWLEDGED AND READ BACK. AT APPROX FL302; ZAU ASKED IF WE WERE DSNDING. WE IMMEDIATELY LEVELED OFF AND ANSWERED IN THE AFFIRMATIVE; AS PER OUR CLRNC. THE CTLR THEN ASKED IF ACR FLT #ABC WAS DSNDING. THE OTHER ACR ANSWERED NEGATIVE. THE CTLR THEN GAVE ACR ABC CLRNC TO FL240 AND WE WERE TO STAY AT FL310. WE RETURNED TO FL310. THE FACTORS THAT MAY HAVE CONTRIBUTED TO THIS INCIDENT; AS WE SAW IT; COULD HAVE BEEN THE PRACTICE OF OPERATING ON MORE THAN 1 FREQ BY THE CTLR. OUR FREQ HAD VERY LITTLE TFC (121.37); BUT IF THE CTLR WAS WORKING OTHER ACFT ON OTHER FREQS; THAT WOULD HAVE CONTRIBUTED TO THE CONFUSION. ANOTHER PRACTICE OFTEN USED; NOT IN THIS CASE; IS TO MAKE ACFT WITH SIMILAR CALL SIGNS AWARE OF EACH OTHER. IN MY OPINION; THAT WOULD CAUSE US TO BE EXTRA VIGILANT. FINALLY; THE READBACK. WE WERE VERY DELIBERATE WITH OUR READBACK OF THE CLRNC PRECEDED WITH OUR CALL SIGN. ABSENT ANY CORRECTION; THAT LEAVES A PERCEPTION THE PROPER ACFT GOT THE PROPER CLRNC. AT NO TIME WAS THERE ANY DANGER BECAUSE THE CTLR BECAME AWARE OF THE SIT EARLY ENOUGH TO PREVENT ANY CONFLICT.