SIMILAR CALL SIGN. ACR X CLB TO OCCUPIED ALT HAD LTSS FROM ACFT Z. SYS ERROR.

Narrative

DURING DEP AND CLB TO CRUISE ALT; ANOTHER ACFT Y HAD RESPONDED SEVERAL TIMES TO CLRNCS TO OUR ACFT ACR X. WE WERE GIVEN PRESENT POS DIRECT MILFORD (MLF) CLB TO 310; TO WHICH ACR Y ACCEPTED OUR CLRNC. WE ADVISED SLC ARTCC OF THE CONFUSION AND RESTATED OUR CLRNC TO MLF AT 310 TO WHICH SLC ARTCC CONCURRED. SEVERAL MINS LATER; PASSING APPROX FL298 WE RECEIVED THE AMENDED ALT OF FL290 DUE TO NBOUND TFC. WE ALSO RECEIVED A TCASII TA OF TFC Z AT FL310. THE CLB WAS STOPPED AND AS WE STARTED AN IMMEDIATE DSCNT; SLC ARTCC GAVE US A TURN OF 30 DEGS TO INCREASE SEPARATION. SLC ARTCC STATED HE HAD HEARD AN ACKNOWLEDGEMENT OF THE FL290 RESTR EARLIER; BUT WE HAD NOT RESPONDED; SO SOMEONE ELSE MUST HAVE READ BACK THE RESTRICTED CLRNC FOR OUR ACFT. SUPPLEMENTAL INFO FROM ACN 268046: CLBING OUT OF SLC TO LAS; ATC ISSUED 2 CLRNCS TO X OF WHICH I ANSWERED; THEN CORRECTED MY MISTAKE WITH CTR. X ALSO ACKNOWLEDGED THE ERROR AND COMPLIED WITH THE CLRNCS. THE CONFUSION OCCURRED BECAUSE OUR INBOUND FLT TO SLC WAS XX AND X WAS DEPARTING IN FRONT OF US. SUPPLEMENTAL INFO FROM ACN 268048: ON CLB OUT FROM SLC THE COPLT ANSWERED A CALL FROM CTR FOR FLT X. I CAUGHT HIS ERROR INSTANTLY AND HE CALLED CTR BACK AND TOLD THEM THAT HE HAD ANSWERED FOR X BUT WE WERE Y.