INSTRUCTOR PLT FILED IFR CLRNC FOR WRONG ACFT RADIO CALL SIGN.

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I WAS PARTICIPATING IN A TRAINING ACTIVITY AT YEAGER FIELD IN CHARLESTON; WV. THERE WERE SEVERAL OTHER ACFT THERE; ALL WITH SIMILAR CALL SIGNS. AFTER THE DAY'S ACTIVITIES (ALL CLASSROOM -- NO FLYING); I OBTAINED A WX BRIEFING AND FILED A VFR FLT PLAN FOR THE RETURN TRIP HOME. THE FSS SPECIALIST REMARKED THAT HE THOUGHT THAT HE ALREADY GAVE A BRIEFING FOR MY ACFT. AFTER PREFLT; MYSELF AND 2 OTHER COMMERCIALLY RATED PLTS BOARDED THE ACFT. AFTER COPYING ATIS; I CALLED CLRNC DELIVERY FOR A VFR FLT TO MRB. WAS TOLD CLRED AS FILED AND GIVEN AN ALT; XPONDER SQUAWK; AND DEP FREQ. I SUBSEQUENTLY CALLED GND AND WAS CLRED TO TAXI TO RWY 33. I TAXIED TO THE HOLD SHORT LINE ON TXWY B AT THE APCH END OF RWY 33. WE HEARD GND CALLING 'ACFT HOLDING IN SEQUENCE' BUT WE DIDN'T RESPOND SINCE HE ALREADY KNEW OUR CALL SIGN AS HE CLRED US TO TAXI. THERE WERE NO OTHER ACFT HOLDING IN FRONT OF US BUT OTHERS WERE TAXIING OUT BEHIND US. AFTER COMPLETING THE RUN-UP; I CALLED THE TWR FOR TKOF CLRNC. WAS PROMPTLY TOLD THAT THE NEXT TIME WE NEEDED TO CALL GND BEFORE TAXIING TO THE RWY. I TOLD THE CTLR THAT I DID RECEIVE TAXI CLRNC FROM GND. HE STATED THAT HE WAS THE GND CTLR AS WELL AS TWR CTLR. I CONFERRED WITH MY FELLOW PLTS ON BOARD WHO CONFIRMED THAT WE WERE GIVEN TAXI CLRNC. THIS WAS RELAYED BACK TO THE CTLR. AFTER TKOF; DEP CTL DIRECTED US TO PROCEED ON COURSE; WHICH WE DID. I THEN OPENED MY VFR FLT PLAN WITH FSS. APCHING 5500 FT MSL; I TOLD DEP CTL THAT I WOULD BE LEVELING OFF AT THAT ALT. THE CTLR QUESTIONED WHY I WAS LEVELING OFF AT THAT ALT ON AN IFR FLT PLAN. I INFORMED THE CTLR THAT I FILED A VFR FLT PLAN; NOT IFR. THE CTLR STATED THAT HE HAD AN IFR FLT PLAN FOR OUR ACFT WITH A NOTATION 'STUDENT PLT' IN THE REMARKS SECTION. I RADIOED BACK AND TOLD THE CTLR THAT I FILED VFR AND THERE WERE NO STUDENT PLTS ON BOARD THIS ACFT. IMMEDIATELY; ANOTHER PLT WHOSE VOICE I RECOGNIZE; CAME ON THE FREQ AND SAID 'SORRY; THAT'S MY FAULT.' AFTER THE FLT; I FOUND OUT THAT THE PLT OF THE SECOND ACFT; WHO NORMALLY FLIES THE ACFT I WAS IN; DID FILE AN IFR FLT PLAN BUT MISTAKENLY USED MY ACFT CALL SIGN WHEN FILING. CONTRIBUTING FACTORS TO THIS SIT INCLUDE: SEVERAL ACFT IN THE AREA WITH SIMILAR CALL SIGN; AND INST PLT FILING A FLT PLAN USING THE WRONG CALL SIGN. IT IS SAID THAT HINDSIGHT IS 20/20. REFLECTING BACK; I SHOULD HAVE QUESTIONED THE FSS SPECIALIST FURTHER WHEN HE MENTIONED THAT HE THOUGHT HE JUST BRIEFED THE PLT OF MY ACFT. I JUST ASSUMED HE WAS CONFUSED WITH PLTS OF MANY ACFT WITH VERY SIMILAR CALL SIGNS CALLING FOR BRIEFINGS AT ABOUT THE SAME TIME. I ALSO SHOULD HAVE BEEN SUSPICIOUS WHEN CLRNC DELIVERY CLRED US 'AS FILED;' HOW DID HE KNOW HOW WE FILED ON A VFR FLT PLAN?