ACR X AND ACR Y DIFFERENT COMPANY SAME FLT NUMBERS. ACR Y RESPONDING TO ATC INSTRUCTIONS FOR ACR X. PLTDEV.

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AS AN ZAB CTLR; I WAS ISSUING INSTRUCTIONS TO ACR X INBOUND TO PHX ON THE STANDARD ARR. THE CLRNC WAS QUITE COMMON. IT CONSISTED OF A DSCNT TO AN INTERMEDIATE ALT. THEN A DISCRETION DSCNT TO THE BOTTOM ALT OF MY SECTOR WITH A SPD RESTRICTION FOR SPACING. I HAD CONSIDERABLE DIFFICULTY GETTING ACR X TO UNDERSTAND THE CLRNC. COMS BTWN US WERE CONFUSED AND EXTENDED OVER SOMETHING THAT SHOULD HAVE BEEN ROUTINE. I CONSIDERED THAT THE RADIOS MAY BE TO BLAME AS FREQ PROBLEMS ARE COMMON ON THIS SECTOR. I FINALLY MANAGED TO COMPLETE THE ISSUANCE OF THE CLRNC TO ACR X AND TURNED HIM OVER TO THE LOW ALT SECTOR. I THEN HEARD ACR Y CALL AND ASK FOR CLARIFICATION OF HIS CLRNC. I DID NOT KNOW WHO ACR Y WAS AND AFTER CHKING ON HIS POS (O/GUP -- WELL AWAY FROM MY SECTOR) I ADVISED HIM TO RETURN TO THAT FREQ. HE WAS CONFUSED AT THIS. I REALIZED; THEN; THAT MY COMS PROBLEM WITH ACR X WAS ACR Y ON MY FREQ BY MISTAKE. TALKING OVER ACR X AND TAKING INSTRUCTIONS DIRECTED TO ACR X WHY ACR X DIDN'T QUESTION WHAT WAS HAPPENING I DO NOT KNOW. SUBSEQUENT REVIEW OF THE VOICE TAPE SHOW THAT WAS INDEED ON THE FREQ ACKNOWLEDGED BY ME AND AT TIMES USING HIS OWN CALL SIGN. WHILE IT IS EVIDENT ON THE TAPE; AFTER THE FACT; IT WAS OBVIOUSLY NOT EVIDENT TO ME AT THE TIME IT WAS GOING ON. ADDITIONALLY; ACR X WHEN ISSUED A FREQ CHANGE BY THE SECTOR PRIOR TO ME TOLD THAT SECTOR THAT SOMEONE ELSE HAD TAKEN THE CHANGE. IT SEEMS IF HE WAS GETTING GARBLED INSTRUCTIONS HE MIGHT HAVE REALIZED WHAT WAS GOING ON AND HELPED ME OUT A BIT. THE PREVIOUS CTLR DID NOT ADVISE ME OF WHAT ACR X HAD SAID BEFORE HE CAME OVER TO MY FREQ.