AN EMB120 FO RPT ON AN ALLEGED ALTDEV RESULTING FROM A REPLY TO SIMILAR SOUNDING CALL SIGN NEAR CTY; FL.

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OUR FLT WAS AT 12000 FT (FILED FOR 16000 FT). A SISTER SHIP WITH SIMILAR SOUNDING CALL SIGN WAS ON FREQ WITH US. (OURS: EAEB; SISTER SHIP: EBAB.) CTR GAVE US A CLB TO 16000 FT. AT 13500 FT ATC CALLED US AND ASKED US WHY WE WERE CLBING. I RESPONDED 'BECAUSE YOU CLRED US TO 16000 FT APPROX 2 MINS AGO.' ATC TOLD US TO LEVEL AT 14000 FT AND THAT THEY DID NOT CLR US OUT OF ALT AT 12000 FT. MY CAPT WAS PLT AT CTLS AND I WAS GIVING THE PAX AN ANNOUNCEMENT AT THE TIME OF THIS INCIDENCE; BUT I ALSO KEPT MY AUDIO MIXER UP THE CENTRAL FREQ AND DISTINCTLY HEARD ATC (ZJX) GIVE OUR SHIP'S CALL SIGN THE CLB CLRNC; WHICH MY CAPT READ BACK AND COMMENCED THE CLB. WHEN I WAS FINISHED WITH MY 20 SECOND ANNOUNCEMENT; I ACKNOWLEDGED THE NEW ALT AND WITHIN SECONDS ATC QUERIED US. ATC WENT OUT OF THEIR WAY TO ENSURE THE CALL SIGNS WERE ENUNCIATED WITH EMPHASIS TO PREVENT FURTHER CALL SIGN CONFUSION. UPON RETURN TO BASE; FLC OF SHIP Y CONFIRMED ATC GAVE US THE CLB CLRNC VERSUS THEM; WHICH PUT US IN A POS TO CLB UP UNDER THEM INTO THEIR FLT PATH. RECOMMENDATION: EMPHASIS TO ENSURE SIMILAR CALL SIGNS ARE REDUCED TO MINIMAL LEVEL POSSIBLE BY CARRIERS. ATC TO EMPHASIZE CALLING ACFT WITH SIMILAR CALL SIGNS WITH GREATER EMPHASIS VERSUS BLINDING SPD. UPON RETURN TRIP (PNS TO MCO); 3 ACFT HAD SIMILAR SOUNDING CALL SIGNS TO OUR; APCHING THE ORL CLASS B AIRSPACE. THIS EVENT WAS DEBRIEFED BY THE CAPT WITH THE CHIEF PLT AT AIRLINES AT ORL.