CLRNC REPLY TO WRONG CALL SIGN. FREQ CHANGE WRONG. ACR ON THE WRONG FREQ ACTS ON A CLRNC FOR ANOTHER (AT THE OTHER RWY) AND TAXIES ONTO AN ACTIVE RWY CAUSING A GAR. RWY INCURSION.

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WE TAXIED TO RWY 8R AT PHX AFTER A RWY CHANGE AND FOUND OURSELVES BEHIND SEVERAL ACFT WITH A BUSY FINAL APCH AND A LOT OF RADIO TFC. APCHING THE #1 SPOT; WE SWITCHED OVER TO TWR (I DO NOT RECALL IF WE WERE DIRECTED TO ANOTHER FREQ AT THIS TIME). LOOKING OUT ON FINAL WE COULD SEE AN ACFT APCHING FOR LNDG AND SINCE A COMPANY ACFT HAD JUST LANDED IN FRONT OF US; SPACING WAS GOING TO BE TIGHT. WITHOUT HESITATION OR FURTHER INQUIRY; WE COMPLETED CHKLIST ITEMS AND TOOK OUR POS OUT ON THE RWY EXPECTING AN IMMEDIATE TKOF CLRNC AS SOON AS THE COMPANY ACFT CLRED THE RWY. THERE WAS THEN RADIO SILENCE AND THE NEXT THING WE HEARD WAS TWR TELLING US WE WERE ON THE WRONG FREQ AND TO CLR. APPARENTLY; WE HAD BEEN ON 118.7 WHICH IS FOR RWY 8L INSTEAD OF 120.9 WHICH CTLS RWY 8R. THE ACFT ON FINAL WAS SENT AROUND WITH ADEQUATE WARNING AND WE SUBSEQUENTLY MADE A NORMAL DEP. LATER; I CALLED THE PHX TWR SUPVR FROM MY DEST AND FOUND OUT AN ACFT WITH A DIFFERENT CALL SIGN WITH A VERY SIMILAR CALL SIGN TO OURS HAD BEEN CLRED FOR TKOF ON 118.7 AND THIS IS WHAT WE ACTED UPON. I ALSO FOUND OUT IT WAS A B-757 WHICH WAS SENT AROUND. THE SIMILARITY IN CALL SIGNS; HVY TFC WITH THE RWY CHANGE; OUR DESIRE TO EXPEDITE THE DEP SINCE WE WERE RUNNING LATE; AND THE ANTICIPATION OF A DEP CLRNC JUST AS THE ACFT WITH A DIFFERENT CALL SIGN WAS CLRED FOR TKOF SET UP THIS UNFORTUNATE SCENARIO.