FLC STARTED TO TAXI WITHOUT CLRNC.

Narrative

CALLED FOR TAXI CLRNC WHILE STILL ON GATE. FREQ WAS BUSY. GND CTL CALLED BACK WITH TAXI CLRNC AND RTE TO TAKE; HOWEVER; CALL SIGN HE USED WAS 1 DIGIT OFF (3 DIGIT CALL SIGN). WE BOTH THOUGHT THE CLRNC WAS FOR US AS THE RTE; RWY; ETC WAS NORMAL AND NATURAL FOR OUR GATE LOCATION AND FIRST FIX AFTER TKOF. WE ACKNOWLEDGED THE CLRNC; BEGAN OUR TAXI; AND ATTEMPTED TO CORRECT OUR CALL SIGN WITH THE CTLR. CTLR WAS VERY BUSY; SO WE CONTINUED THE TAXI; REALIZING THE CTLR MISSED THE CALL SIGN. BOTH OF US FIGURED THIS WAS JUST ANOTHER SIMPLE MISTAKE OF MISSING A CALL SIGN DIGIT. SHORTLY AFTER MOVING OUT FROM GATE; AND AFTER PASSING SEVERAL TXWY INTXNS; WE REALIZED THAT THE CLRNC WE TOOK WAS FOR ANOTHER ACFT AT A GATE ON THE SAME CONCOURSE WITH THE SAME INITIAL FIX AS OURS; PUTTING HIM ON THE SAME DEP RWY AS US. THE CTLR FINALLY CAUGHT UP WITH OUR FLT AND REALIZED WHAT WE HAD DONE. WE DID NOT CROSS ANY RWYS AND DID NOT CUT OFF ANY OTHER TFC. WE TOLD GND CTL EXACTLY WHAT WE HAD DONE; THAT WE WERE IN ERROR AND SORRY FOR ANY PROBS AND MIX-UPS. HE THEN RESEQUENCED OUR FLT AND ISSUED TAXI CLRNC AND A HDOF TO TWR. WE ROUTINELY FLY THROUGH BUSY AIRLINE HUBS AND MISSING A CALL SIGN DIGIT IS A COMMON OCCURRENCE BY BOTH CTLRS AND CREWS ALIKE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE ATR-72 FOR A LARGE REGIONAL ACR. HE IS BASED TEMPORARILY IN MIA; AWAY FROM HIS HOME BASE OF ORD. HE AND THE FO ARE GOOD FRIENDS. THE RPTR 'TRUSTS HIM COMPLETELY.' WITH ANY OTHER FO; THE CAPT 'MIGHT HAVE STOPPED THE ACFT AND CHKED THE CLRNC.' THE OTHER ACFT WAS OF THE SAME ACR; SAME TYPE ACFT; SAME RWY; AND SAME INITIAL FIX. THE TRIP NUMBERS WERE JUST 1 DIGIT OFF. GND CTL SEEMED TO UNDERSTAND WHAT THE PROB WAS AND WAS NOT UPSET. THE RPTR HAD NOT CROSSED ANY RWYS OR CUT OFF ANY OTHER ACFT. THE RPTR REALIZES THAT THE ONLY WAY TO PREVENT THIS WOULD BE TO FORCE HIS WAY INTO GND CTL TO VERIFY THE CLRNC.