SIMILAR CALL SIGNS ACR X REPLY TO WRONG CALL SIGN CLB THROUGH ASSIGNED ALT.

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I WAS THE PNF (FO) ON ACR OOX PHX-SAN. RECEIVED CLB CLRNC FROM ZAB TO CLB TO FL230 EXPECT FURTHER CLB AFTER WE PASS A KING AIR AT FL240; 5 MI W OF BXK VOR. WE WERE 15 NM NE OF GBN VOR WHEN I THOUGHT I HEARD ZAB CLR ACR OOX TO FL310 EXPEDITE THROUGH FL270. I READ BACK THE CLRNC AND ZAB DIDN'T DISPUTE MY READBACK. AS WE WERE CLBING THROUGH FL210 I HEARD ACR X3X FOR THE FIRST TIME ASK FOR A VERIFICATION OF HIS CLRNC. ACR X3X RADIO XMISSION CAME ABOUT 45 SECONDS TO 1 MIN AFTER I READ BACK MY CLRNC. THERE WAS A LONG PAUSE FROM ZAB SO I ASKED ZAB TO REVERIFY MY CLRNC. AGAIN; A LONG PAUSE ON THE RADIO; SO I REREAD MY CLRNC TO ZAB. AT THIS TIME WE WERE CLBING THROUGH FL230. I THEN TOLD THE CAPT TO LEVEL OFF UNTIL WE FIND OUT WHICH COMPANY FLT HAD THE CLB CLRNC. WE LEVELED OFF AT 23800 FT AND ZAB TOLD US TO MAINTAIN FL230 BECAUSE OF KING AIR TFC AT FL240. SUGGESTIONS: THE CAPT AND I BOTH THOUGHT ZAB CLRED US TO FL310. WE BOTH NEED TO LISTEN A LITTLE CLOSER WHEN SIMILAR CALL SIGNS ARE ON THE SAME FREQ. SUPPLEMENTAL INFORMATION FROM ACN 265651: ACR FLT X AND X3X ON SAME FREQ (OUR FLT X WAS CLRED TO FL230). WE HEARD AND READ BACK FLT X CLB TO FL310 EXPEDITE THROUGH FL270. LIKE SOUNDING CALL SIGNS ARE A CONTINUING PROB. THIS PLT TRIES TO ALWAYS BE ALERT; BUT SOMETIMES IT STILL CAN HAPPEN. ATC SHOULD NOTIFY LIKE SOUNDING CALL SIGNS.