FLC RESPONDED TO ANOTHER ACFT'S DSCNT CLRNC.

Narrative

WE WERE ENRTE FROM BUR TO SJC; ESTABLISHED ON THE ROBLE 2 ARR N OF THE AVENAL VOR XING AT FL350. ZLA GAVE A CLRNC FOR PLT'S DISCRETION DSCNT TO FL240. THE CAPT AND I BOTH HEARD OUR FLT NUMBER. IT WAS READ BACK AND WE BOTH ACKNOWLEDGED IT AS THE NEW ALT WAS SELECTED IN THE MCP. APPROX 5-6 MINS LATER; I BEGAN THE DSCNT TO FL240. AT FL345 ATC SAID 'VERIFY YOU ARE AT FL350.' THE CAPT REPLIED 'WE HAVE STARTED DOWN TO FL240.' ATC REPLIED 'NEGATIVE; THAT CLRNC WAS FOR SOMEONE ELSE; CLB AND MAINTAIN FL350.' WHILE DSNDING AT APPROX FL345 WE ALSO RECEIVED AN RA FROM OUR TCASII. IT WAS OPPOSITE DIRECTION TFC AT FL330 (AN MD80). (I HAD ALREADY BEGUN MY CLB BACK TO FL350 AT THIS TIME. WE DID NOT GO ANY LOWER THAN FL342 DURING OUR RECOVERY.) WE HAD VISUAL CONTACT WITH THE TFC AS IT PASSED 1 - 1 1/2 MI TO OUR L AT FL330. WHEN WE CHKED ON FREQ; WE WERE NEVER CAUTIONED FOR A SIMILAR SOUNDING CALL SIGN IN USE. HAD ATC ADVISED US OF THIS INFO; IT WOULD HAVE HELPED US CONSIDERABLY. ONCE ON THE GND IN SAN JOSE WE CALLED ZLA BY PHONE. WHILE TALKING WITH THE ATC SUPVR HE TOLD US THAT COMPANY FLT HAD ADVISED HIS NEXT ATC CTLR THAT THEY THOUGHT SOMEONE ELSE HAD ACKNOWLEDGED THEIR DSCNT CLRNC TO FL240. WE WERE NEVER ADVISED OR CAUTIONED; AND THERE WAS NEVER ANY QUESTIONS FROM ATC AS TO WHETHER WE OR ANYONE ELSE HAD UNKNOWINGLY TAKEN THE WRONG CLRNC. I BELIEVE THAT HAD ATC CAUTIONED US OF THE SIMILAR CALL SIGN; THIS DEV WOULD HAVE BEEN AVOIDED.