AN F900 CREW; TAXIING FOR TKOF AT MDW; ANSWERED FOR AND RESPONDED TO A CLRNC GIVEN TO ANOTHER ACFT WITH A SIMILAR CALL SIGN.

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UPON CALLING GND WE WERE ONCE AGAIN INFORMED THE GND STOP WAS BACK ON; AND THE CTLR ASKED IF WE WOULD LIKE TO STAY ON THE RAMP OR TAXI OUT TO THE RWY. THINKING IT WOULD BE BEST TO GET IN LINE; AND THINKING IT WOULD BE A SHORT DELAY; WE ELECTED TO TAXI OUT TOWARD THE RWY. WE WERE DIRECTED OUT ONTO RWY 31R WHERE WE JOINED OTHER ACFT THAT WERE ALSO WAITING TO DEPART. AFTER SITTING FOR 2 HRS 10 MINS; EVERYONE INVOLVED; INCLUDING THE CTLRS; WERE GETTING A LITTLE STRESSED OUT. THE COM WAS POOR AT BEST AS TO THE ORDER OF ACFT LEAVING BECAUSE THEY WERE PARKED EVERYWHERE. AS THE PLANES AHEAD OF US STARTED MOVING; WE RESTARTED OUR ACFT AND SLOWLY TAXIED FORWARD. TWR THEN TOLD US TO TAXI UP TO THE HOLD LINE AND THAT WE'D BE THE 'NEXT TO GO.' AN ACFT LANDED ON OUR RWY AND TWR TOLD WHAT WE THOUGHT WAS OUR ACFT TO TAXI INTO POS AND SAID; 'THERE IS AN ACFT ON 3 1/2 MI FINAL -- BE READY TO GO.' I REPLIED TO THE INSTRUCTIONS AND WE STARTED MOVING. OUR ACFT WAS 1/2 WAY ACROSS THE HOLD LINE WHEN TWR TOLD US TO STOP AND THAT THE PREVIOUSLY ISSUED CLRNC WAS NOT FOR US. TWR THEN CLRED ACFT Y FOR TKOF. WE STAYED WHERE WE WERE; WAITED FOR BOTH ACR Y ACFT TO DEPART AND ANOTHER AIRLINER TO LAND; AND THEN FINALLY WERE GIVEN CLRNC TO TAKE OFF. NOTHING ELSE WAS MENTIONED AND THE FLT CONTINUED ONTO GRAND RAPIDS UNEVENTFULLY. THIS WAS A VERY FRUSTRATING SIT FOR ME; ESPECIALLY WITH THE CONCENTRATED EFFORT TO REDUCE RWY INCURSIONS. I HAVE REPLAYED IT MANY TIMES IN MY HEAD TRYING TO DETERMINE THE EXACT CAUSE. I'VE CONCLUDED THERE WAS NO ONE CAUSE; BUT MANY FACTORS THAT COMBINED TO MAKE A SIT OCCUR. I THINK THE SIMILARITY OF OUR CALL NUMBERS WAS THE BIGGEST CONTRIBUTOR. I'M NOT SURE IF THE CTLR MIXED UP OUR CALL SIGNS WITH ACFT Y JET OR IF I BECAUSE OF THE 'GO-MODE' DID NOT HEAR THE CALL SIGN CORRECTLY. FORTUNATELY; THE CTLR SAW WHAT HAPPENED AND CORRECTED IT BEFORE ANYTHING MORE SERIOUS HAPPENED. I PRIDE MYSELF ON BEING A PROFESSIONAL PLT; AND HAVE TAKEN THE RWY INCURSION SAFETY PROGRAM VERY SERIOUSLY. A SIT LIKE THIS IS VERY HUMBLING AND JUST PROVES YOU CAN NEVER BE TOO CAREFUL AND WHEN IN DOUBT ALWAYS CLARIFY.