DC9 CREW AND ZMP CTLRS WERE CONFUSED BY ACFT WITH SIMILAR CALL SIGN.

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GIVEN CLRNC FROM 35000 FT TO 24000 FT; PLT'S DISCRETION. SEVERAL OTHER FLTS WITH SIMILAR CALL SIGNS AND A CTLR RECEIVING TRAINING; BY VOICE COMING THROUGH TELLING HIM THINGS TO SAY. OUR FLT WAS #ABCD; A FERRY FLT. WE KEPT HEARING A CALL TO ABCE; BCE; ETC. ABCE WAS GIVING CLRNC TO CROSS TWINZ ON EAU CLARE FOUR ARR AT 11000 FT. WE WERE PLT'S DISCRETION TO 24000 FT. AT EAU VOR WE WERE QUESTIONED ON OUR ALT. REPLY WAS 28000 FT AND DSNDING. AT 27500 FT; 15 SECONDS LATER; ASKED AGAIN OUR ALT. THEN GIVEN A TURN N; E; S; THEN W TO REJOIN WITH DSCNT CLRNC TO 14000 FT; THEN FINALLY 11000 FT AT TWINZ. SEVERAL ACFT WERE USING SIMILAR CALL SIGNS; NOT ONLY OURS; BUT OTHER AIRLINES. WE GOT CAUGHT UP IN THE CONFUSION WITHOUT A CLRNC FOR OUR CALL SIGN. THE CTLR NEVER QUESTIONED US BUT JUST GAVE US VECTORS TO GET DOWN. HE HAD HIS HANDS FULL AT THIS TIME; AND EITHER WE MISSED HIS DSCNT CLRNC BY THE CALL SIGN CONFUSION OR IT WAS NEVER ISSUED TO OUR CALL SIGN. AT LEAST WE NEVER HEARD ONE. CERTAIN TIMES OF THE DAY ARE WORSE THAN OTHERS; BUT I WOULD THINK WE COULD COME UP WITH A NUMBERING SYS THAT WOULD TAKE AWAY FROM THE CHANCES OF THIS HAPPENING. SIMILAR CALL SIGNS ARE ALWAYS GOING TO BE OUT THERE; BUT THEY SHOULD NOT BE AT THE SAME AIRLINE.