FLC OF BE300 MISINTERPS DEP INSTRUCTIONS AND DEPARTS WITHOUT CLRNC. WHEN CONTACTING DEP AFTER AIRBORNE THEY ARE QUESTIONED AS TO WHY NO CONTACT PRIOR TO DEP.

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WITH THE CAPT TAXIING THE ACFT; I PICKED UP AN IFR CLRNC WITH APCH CTL. OUR CLRNC WAS UNUSUAL BECAUSE IT DID NOT REQUIRE US TO FLY THE SID. THE RWY I ASKED APCH FOR CONFIRMATION THAT WE DID NOT HAVE TO FLY THE SID. THE CTLR SAID 'NO DEP PROC; CLB AND MAINTAIN 15000 FT; AND CALL AIRBORNE.' AT LEAST WE THOUGHT HE SAID CALL AIRBORNE. WE TOOK OFF ON RWY 18 AND OUT OF 500 FT AGL I CALLED APCH. THE CTLR IMMEDIATELY ASKED US WHY WE HAD NOT TOLD HIM WE WERE READY BEFORE DEPARTING. I TOLD HIM THAT THE CAPT AND I BOTH THOUGHT HE RELEASED US WITH THE LAST XMISSION. THE CTLR SAID HE DID NOT RELEASE US; AND FOR FUTURE REF ALWAYS CALL HIM BEFORE DEPARTING. THE WX WAS VFR AND THERE WAS NO TFC CONFLICT; SO THINGS COULD HAVE BEEN A LOT WORSE. AFTER DISCUSSING THE SIT; THE CAPT AND I CONCLUDED THAT THE CTLR PROBABLY DID NOT RELEASE US FOR DEP. WE ASSUMED WE WERE RELEASED BECAUSE HE TOLD US TO CLB AND MAINTAIN 15000 FT; AND WHAT WE THOUGHT WAS 'CALL AIRBORNE' WAS ACTUALLY 'CALL READY.' FROM NOW ON I WILL BE EXTRA VIGILANT TO HEAR WHAT THE CTLR SAYS -- NOT WHAT I WANT HIM TO SAY.