FLC INADVERTENTLY STARTED DSCNT ON AN ILS APCH PREMATURELY DUE TO MISINTERP OF SIMILAR SOUNDING CALL SIGNS.

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CLRED FOR ILS APCH TO RWY 11R AT 5000 FT. STARTED DSCNT ON THE GS AND AT ABOUT 4000 FT LOST THE GS SIGNAL. COPLT CALLED APCH CTL AND RPTED LOSS OF GS. I THOUGHT I HEARD CLRED TO 3000 FT. WE DISCOVERED AFTER DSNDING BELOW THE STEP DOWN ALT TO WAYZA (4000 FT) THAT APCH CTL NEVER RESPONDED TO US. (THERE APPARENTLY WAS ANOTHER CARRIER IN THE AREA WITH A SIMILAR CALL SIGN). AT THAT POINT WE WERE VMC AND REMAINED AT 3000 FT UNTIL NEAR KINNS. BY THEN THE GS HAD BEEN RESTORED AND WE REINTERCEPTED THE GS FOR AN UNEVENTFUL VISUAL ILS APCH AND LNDG. IF MSP APCH CTL NOTICED OUR DSCNT BELOW 4000 FT BEFORE WAYZA THEY NEVER MENTIONED IT. ATC IS STILL THE WORST OFFENDER USING INCOMPLETE CALL SIGNS. ATC IS STILL THE WORST OFFENDER NOT ANSWERING OR ACKNOWLEDGING CALLS TO THEM. ALL CREWS STILL CANNOT RELAX AND TAKE ANYTHING FOR GRANTED. IF ANYTHING IS INCOMPLETE OR UNCLR OR IN ANYWAY THE SLIGHTEST IN DOUBT. DO NOT PROCEED UNTIL IT'S CLARIFIED EVEN IF THEY IGNORE YOUR CALLS. AFTER ALL THESE YEARS I THOUGHT I KNEW THAT; BUT YOU CAN GET TOO COMFORTABLE AFTER AWHILE.