CAPT OF AN ACR MLG STOPPED DSCNT AND QUESTIONED THE APCH CTLR AFTER SUSPECTING A RESPONSE TO ANOTHER ACFT SIMILAR SOUNDING CALL SIGN. CTLR THEN CLRED THE CAPT'S ACFT TO A LOWER ALT.

Narrative

I WILL START WITH THE CAUSE; THAT BEING SIMILAR SOUNDING CALL SIGNS. I KNOW ACRS ARE PRESSED DUE TO THE NUMBER OF FLTS OPERATING IN ANY GIVEN DAY: SCHEDULED; CHARTERED; FERRY; ETC. WHETHER THE FO WORKING THE ATC RADIO ACTUALLY HEARD AND ANSWERED A WRONG CALL SIGN (WHICH I DO NOT THINK WAS THE CASE); OR THE ATC CTLR MISHEARD THE READBACK; SIMILAR ACFT CALL SIGNS BTWN ACR X ACFT; ACR Y ACFT (AND OTHER MAJOR CARRIERS) IS A CONSTANT PROB. WE INADVERTENTLY VACATED OUR ASSIGNED ALT FOR ANOTHER ASSIGNED ALT BUT I HAD A 'BAD' FEELING THAT SOMETHING WAS NOT RIGHT. APCHING FROM THE SE AND LNDG TO THE S (RWY 21L IN DTW) GENERALLY REQUIRES YOU TO MAINTAIN 12000 FT OR SOMETIMES 11000 FT MSL UNTIL ABEAM THE DXO VOR/DTW ARPT. WHY DID THE CTLRS CLR US DOWN TO 3000 FT MSL 25 MI SE OF THE ARPT? I HAD STARTED 'DOWN' AS YOU WOULD NORMALLY; WHEN ASSIGNED A NEW ALT. THEN THAT 'BAD' FEELING HIT. I KNEW SOMETHING WAS NOT RIGHT. BEING FAMILIAR WITH THE DETROIT PROCS; I IMMEDIATELY QUERIED THE CTLR. 'DSND AND MAINTAIN 11000 FT MSL;' HE SAID. I PROMPTLY COMPLIED. NO TFC CONFLICT EVER OCCURRED AND THE FLT UNEVENTFULLY CONTINUED. WE; OF COURSE; WERE AT THE TIME BUSY WITH DSCNT AND APCH CHKS; 'BRIEFING' FOR THE APCH IN USE; AS WELL AS DISCUSSING THE NEED/TERMINATION OF WING AND ENG ANTI-ICE. I KNOW HOW BUSY THE ATC CTLR WAS; JUDGING BY THE FREQ CONGESTION! READBACKS ARE IMPORTANT -- WE ALL MUST LISTEN AND SLOW DOWN OUR VERBIAGE. I OBVIOUSLY WOULD NEVER CLB OR DSND WITHOUT CLRNC. MAYBE OUR CALL SIGNS NEED TO BE SUFFIXED WITH A LETTER; IE; ACR-Z ABC.