A DC10 FLC ACCEPTS AN ACARS XMITTED DATA LINK OCEANIC CLRNC FROM EGGX CTL THAT WAS MEANT FOR THE COMPANY FLT 2 HRS BEHIND WITH A SIMILAR NUMERIC CALL SIGN. SUBJECT FLT HAD A NUMERIC APPENDAGE.

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DISPATCHED AS FLT XYZ BECAUSE OF CANCELLATION ON PREVIOUS DAY. HAD 'COMPANY' FLT XY 2 HRS BEHIND US (SCHEDULED). WE WERE RELEASED AS XY ON TUESDAY FOR COMPANY ACARS AND FLT XY ON WEDNESDAY WAS DISPATCHED BEHIND US. WE USED FLT XYZ FOR ALL RADIO CALLS AND CLRNCS FROM FRANKFURT. REQUESTED OCEANIC CLRNC FROM SHANWICK ON ACARS 75 MINS PRIOR TO OCEANIC ENTRY POINT. RECEIVED CLRNC AS FILED; BUT WHEN VIEWING THE ACCEPTED CLRNC MESSAGE WE REALIZED THAT THE CLRNC WE RECEIVED MAY HAVE BEEN FOR THE FLT DEPARTING BEHIND US (FLT XY) AND NOT FOR FLT XYZ. COPLT ESTABLISHED VOICE COM ON 123.95 TO CLARIFY SIT. WE WERE TOLD TO FLY OUR CLRNC AFTER WE HAD VERIFIED ON VOICE AND ACARS SYS WOULD BE RESET FOR THE COMPANY ACFT THAT WAS BEHIND US SO THEY COULD RECEIVE DATA LINK CLRNC ALSO. WHEN WE REALIZED THAT THIS COULD BE A PROB IN THE FUTURE; WE SENT DISPATCH A MESSAGE AND FILED A COMPANY PINK SHEET. FLT CONTINUED TO DTW. THIS PROB CAN BE AVOIDED IN THE FUTURE BY MAKING SURE ACARS IS NOT USED FOR DATA LINK OCEANIC CLRNCS FOR FLT WITH AN ALPHA-ATTACHED (2 FLT NUMBERS SIMILAR AIRBORNE AT THE SAME TIME). ALTHOUGH WE MAY HAVE ACCEPTED CLRNC FOR ANOTHER ACFT; THE SIT WAS RESOLVED WELL BEFORE REACHING OUT OCEANIC ENTRY POINT WHERE THE NEW CLRNC STARTED. THE REMARKS SECTION OF THE COMPANY FLT PLAN SHOULD INCLUDE CAUTION ABOUT THE ACARS DATA LINK AND SUGGEST THESE CLRNCS BE OBTAINED VIA VOICE ONLY.