APCH RADAR CTLR AT OAK BECOMES CONFUSED WITH SIMILAR CALL SIGNS AND INSTRUCTS THE WRONG ACFT TO CHANGE FREQ.

Narrative

COMPANY ACFT WITH SIMILAR CALL SIGN (ACFT YXZ) PRECEDED OUR ACFT (CALL SIGN ACFT XYZ) INTO BAY AREA. CTLRS; STARTING BACK AT ZSE; CAUTIONED BOTH ACFT ABOUT SIMILAR CALL SIGNS. OUR FLT WAS 'COMPANY ACFT X-Y-Z (SINGLE DIGITS)' VERSUS 'COMPANY ACFT YXZ (GROUP FORM)' TO ENSURE CORRECT RECOGNITION BY BAY APCH. RECEIVED BOTH ACFT (Y GOING TO SJC; AND X GOING TO SFO IN SUCCESSION). AFTER SEVERAL COMS TO ACFT Y; OTHER ACFT AND ACFT X; ACFT X RECEIVED CLRNC TO FLY HDG 110 DEGS; DSND TO 6000 FT AND CHANGE TO APCH 120.1. CLRNC READ BACK AND ACKNOWLEDGED. UPON CHK-IN; WAS TOLD TO RETURN TO PREVIOUS FREQ AND MAINTAIN CURRENT ALT. RETURNED TO PREVIOUS FREQ. CTLR AGAIN ISSUED CLRNC TO OUR ACFT THINKING IT WAS ACR Y AHEAD. FINALLY; SWITCHED ACR X TO ANOTHER CTLR AND NO FURTHER PROBS. SIMILAR CALL SIGNS PUTS UNNECESSARY RISK ON ALL PARTIES. CORRECTION LIES WITH COMPANY ENSURING THIS DOES NOT HAPPEN; IE; CHANGE ONE OR BOTH CALL SIGNS. COMPANY HAS SUCH A PROGRAM; HOWEVER; IT DOES NOT GET ENOUGH EMPHASIS UNTIL A PROB IS RPTED.