AFTER A PLT REQUESTED A SUGGESTED ROUTING AND BEING TOLD TO HOLD FOR RELEASE ATC ASSUMES AN IFR CLRNC IS TO BE GIVEN. THE TKOF IS MADE VFR WITH THE EXPECTATION OF AN INFLT FILING OF THE CLRNC. ATC IS NOT HAPPY AND THE PLT THINKS HE HAS DONE NOTHING WRONG.

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ON THE GND I CALLED CLRNC DELIVERY TO OBTAIN OUR ROUTING. ON INITIAL CALL; I ADVISED THAT I WANTED OUR ROUTING; NOT AN ACTUAL CLRNC. AT THAT TIME; WE WERE STILL 30 MINS FROM ENG START. SOUTH BEND ADVISED ME TO HOLD FOR RELEASE. THE PAX ARRIVED SOON AFTER; BEFORE THEY WERE EXPECTED. WE QUICKLY LOADED THE AIRPLANE AND BEGAN TO TAXI. TAXI CHKLIST WAS COMPLETED AS WE APCHED THE RWY; SO WE DEPARTED VFR; PLANNING TO PICK UP OUR IFR CLRNC IN THE AIR. SOUTH BEND WAS UPSET; SAYING WE HAD DEPARTED ILLEGALLY UNDER IFR. WE WERE SQUAWKING VFR AND WERE CLBING TO A VFR ALT UNTIL WE RECEIVED CLRNC. I NORMALLY WOULD'VE CALLED FOR GND CLRNC; BUT I THOUGHT WE HAD THE OPTION OF DEPARTING VFR. IF THE INCIDENT HAD OCCURRED IN IMC; THAT WOULD BE AN OBVIOUS VIOLATION. WHEN CLRNC ADVISED ME TO HOLD FOR RELEASE; MY ASSUMPTION WAS WE HAD TO HOLD FOR AN IFR RELEASE. I DID NOT REALIZE WE HAD TO HOLD REGARDLESS. I HAVE NOT YET FOUND AN FAR THAT ADDRESSES THIS SIT; OTHER THAN NOT DEVIATING FROM AN ATC CLRNC. THE MAIN FACTORS IN THIS SIT WAS TIME PRESSURE; AS WELL AS CONFUSION ABOUT THE FARS.