INST RATED PVT PLT TKOF PRIOR TO BEING RELEASED ON IFR FLT PLAN FROM NON CTLED ARPT.

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FILED AN IFR FLT PLAN FROM GTU TO T82 (FREDERICKSBURG; TX); TAXIED TO RUN-UP AREA FOR RWY 11. CALLED CLRNC DELIVERY AND RECEIVED CLRNC WITH INITIAL HDG AND 4000 FT ALT (EXPECTED ALT 6000 FT); AND DEP FREQ AUSTIN. TOLD #1 FOR DEP AND HOLD FOR RELEASE. THERE WERE 2 PLANES IN THE PATTERN (TOUCH-AND-GOES). WHEN AN OPENING OCCURRED; I ANNOUNCED MY INTENTIONS; DEPARTING RWY 11 AND TAXIED ONTO RWY AND DEPARTED. I REALIZED RIGHT AFTER DEPARTING THAT I HAD NOT BEEN RELEASED. I MAINTAINED VFR AND CALLED AUSTIN DEP SEVERAL TIMES AND TOLD THEM I HAD DEPARTED AND WAS UNABLE TO REACH DEP. THEY TOLD ME TO CLB AND MAINTAIN VFR AND I SHOULD BE ABLE TO REACH AUSTIN DEP. I WAS FINALLY ABLE TO REACH AUSTIN AND WAS TOLD I HAD NOT BEEN RELEASED FOR DEP. THEY GAVE ME MY CLRNC TO T82 AND I MADE THE FLT. AFTER LNDG; I CALLED AUSTIN TWR AND SPOKE TO THE SUPVR IN THE RADAR ROOM AND APOLOGIZED. HE THANKED ME FOR CALLING AND SAID HE WOULD PASS IT ON TO THE CTLR. POSSIBLE SOLUTION: INSTEAD OF LANGUAGE 'HOLD FOR RELEASE' USE 'DO NOT DEPART -- AT THIS TIME -- HOLD FOR RELEASE.' MAIN CAUSES: 1) MY DISTR BY OTHER PLANES IN PATTERN AND FITTING IN. 2) MY NOT FULLY LISTENING TO CLRNC. 3) LANGUAGE USED FOR HOLD FOR RELEASE (MINIMAL FACTOR: I SHOULD HAVE UNDERSTOOD). WHEN TOLD #1 FOR DEP; I INTERPED IT AS READY FOR DEP.