ACR CAPT ACKNOWLEDGED AND EXECUTED A CLB CLRNC FOR A SIMILAR SOUNDING COMPANY CALL SIGN; RESULTING IN ATC AND CREW CONFUSION. COMPANY SHOULD EVALUATE SIMILAR CALL SIGNS AND RTES TO ELIMINATE THESE OCCURRENCES.

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ON JUL/XX/96 AT XX13 WE DEPARTED LAX FOR SEA AS ACR 111. CLRNC TO SEA WAS VIA GORMAN 1 DEP; SHAFTER (EHF) TRANSITION; J5 AS FILED. NUMEROUS RESTR TO ALTS WERE RECEIVED DURING DEP FROM DEP CTL AND SOCAL WITH A FINAL ALT RESTR OF 15000 FT FROM SOCAL ON 125.8. IN THE VICINITY OF EHF SOCAL (125.8) HANDED US OFF TO ZLA ON 128.37. WE CHKED IN AS ACR 111 AND WERE ADVISED OF TFC AT 3 O'CLOCK WBOUND AND RECEIVED NUMEROUS ALT RESTRS FROM 15000 FT TO FL220. PRIOR TO FL220 ZLA (128.37) ADVISED 'ACR 111' TO CONTACT ZOA ON 132.8. CHKING IN WITH ZOA 'ACR 111 WITH YOU OUT OF FL215 FOR FL220' AND WERE ADVISED 'MAINTAIN FL310;' WHICH WAS READ BACK AS 'ACR 111 CLB AND MAINTAIN FL310.' SHORTLY AFTER (APPROX 5-10 SECONDS) 'ACR 211 IS LEVEL FL310' WAS SAID ON FREQ (132.8) WITH NO RESPONSE FROM THE CTLR. I QUESTIONED 'CONFIRM ACR 111 IS CLRED CLB AND MAINTAIN FL310.' ZOA'S REPLY WAS 'NEGATIVE; YOU ARE NOT TO BE ON THIS FREQ. YOU TOOK ACR 211 HDOF; RETURN TO YOUR PRIOR FREQ.' OUR ALT WAS FL243 WHICH WE MAINTAINED. RETURNING TO ZLA ON 128.37 WE ADVISED THAT APPARENTLY WE MISTOOK ACR 211 HDOF AND WERE MISTAKENLY ASSIGNED A HIGHER ALT AND WE ARE LEVEL AT FL243 AND WHAT ALT SHALL WE MAINTAIN? ZLA CTR ADVISED US TO RETURN TO ZOA ON 132.8. RETURNING TO 132.8 WE WERE ADVISED TO MAINTAIN FL310. ADDITIONAL INFO: 1) ACR 211 DEPARTED SAN DIEGO FOR SEA ABOUT 20 MINS PRIOR TO OUR LAX DEP WHICH PUT ACR 211 AND ACR 111 IN COMMON CTR SECTORS AND FREQS. 2) AS WE FOLLOWED ACR 211 FROM LAX TO SEA; WE WERE USUALLY 3-5 MINS BEHIND ON HDOF AND NEVER ADVISED OF COMMON CALL SIGNS OR WHEN WE CAME ON COMMON ATC FREQS WITH SIMILAR CALL SIGNS. I BELIEVE 1) ZLA 128.37 CONFUSED OUR CALL SIGN AND CLRED ACR 111 TO ZOA 132.8. 2) WE CHKED IN ON OAK 132.8 WITH A FULL CALL SIGN AS 'ACR 111' OUT OF 21500 FT FOR FL220. EVEN IF WE MISTOOK ACR 211 HDOF; WHEN CHKING IN WITH ZOA AS ACR 111 AT A LOWER ALT 21500 CLBING TO AN ALT BELOW FL310 (FL220) WITH ACR 211 ALREADY LEVEL AT FL310 TOO MANY THINGS WERE NOT RIGHT TO GIVE US ANY NEW CLRNC UNTIL CONFIRMING WHO IS WHO.