AN ACR B737 FLC COPIED AND COMPLIED WITH ANOTHER ACFT'S CLRNC TO CROSS AN ACTIVE RWY.

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FLT FROM CHICAGO TO BOSTON WITH NIGHT LNDG AT BOS. LANDED RWY 22L; HOLD SHORT OF RWY 27. WE TURNED OFF AT TXWY C AND CONTACTED BOS TWR ON 128.8. MALE CTLR INITIALLY TOLD US TO 'HOLD SHORT OF RWY 22R;' THEN TOLD US TO CROSS; AND THEN TOLD TO 'HOLD SHORT' DUE TO TFC EXITING THE CONCOURSE RAMP WHICH WOULD HAVE PREVENTED OUR ENTRY TO THE GATE AREA. THERE WAS A DELAY OF SEVERAL MINS; DURING WHICH TIME WE MADE A PA ANNOUNCEMENT TO THE PAX. NEXT THING I HEARD WAS THE LAST PART OF A CLRNC TO CROSS RWY 22R; 'CLRED TO CROSS WITHOUT DELAY; FAST TFC ON A 2 NM FINAL.' THE COPLT IMMEDIATELY READ BACK THE CLRNC; THAT WE WERE 'CLRED TO CROSS RWY 22R; WITHOUT DELAY.' THIS CLRNC WAS GIVEN BY A DIFFERENT/FEMALE CTLR; AND WAS A BIT SURPRISING SINCE I HAD NOT YET SEEN THE TFC EXIT THE CONCOURSE RAMP. SINCE I HAD HEARD ONLY THE LAST PORTION OF THE XMISSION; AND NOT THE CALL SIGN; I TURNED AND ASKED THE COPLT; 'ARE YOU POSITIVE THAT IT WAS FOR US?' HE REPLIED IN THE AFFIRMATIVE AND WE CROSSED RWY 22R WITHOUT DELAY. THE CTLR WAS ALREADY TALKING TO SOMEONE ELSE SO I HAD TO DEPEND ON THE COPLT. HE WAS WRONG! AS WE CROSSED; WE COULD SEE TFC STILL BLOCKING THE ALLEYWAY. ANOTHER ACFT ON THE PARALLEL TXWY HAD TO STOP AND GIVE WAY SO WE COULD CLR THE HOLD LINE. GND CTL HAD NO IDEA WHAT TO DO WITH US AND ENDED UP 'BOXING' US AROUND TO GET US OUT OF EVERYONE'S WAY. WHEN WE SWITCHED TO GND CTL; WE HEARD THEM TALKING TO ANOTHER ACFT; POSSIBLY A CALL SIGN THAT WAS SIMILAR. IN FACT; THE COPLT ANSWERED TWICE FOR THEM. I'M CONVINCED THAT WE CROSSED RWY 22R BASED ON A CLRNC GIVEN TO AN ACFT WITH A SIMILAR CALL SIGN. A TELEPHONE CALL TO BOSTON CONFIRMED MY SUSPICION. TRUST IS A FRAGILE COMMODITY. RELIANCE ON CREW CONCEPT IS ONLY AS GOOD AS EACH MEMBER. YOU ARE EITHER ALL WRONG OR YOU ARE ALL RIGHT. NEXT TIME I ASK TWICE; MAYBE 3 TIMES.