AN EMS FLC CLBS INTO THE APCH CORRIDOR OF A MAJOR ARPT AFTER SOME CONFUSION OVER THEIR ROUTING AND ALT ASSIGNMENT AS GIVEN BY ZZZ TWR. DEP CTLR ADVISES THEM OF THEIR PREMATURE CLB AND VARIANCE FROM THE SID DEP PROC.

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I WORK FOR HOSPITAL FLYING AN EMS HELI. WE HOLD OUR OWN FAR PART 135 ACR CERTIFICATE. WE OPERATE OUR ACFT SINGLE PLT IFR AND VFR. ON THIS PARTICULAR EVENING; I DECIDED TO ACCOMPANY THE DUTY PLT ON A PATIENT TRANSPORT DUE TO HIS RECENT HIRE. HE WAS NEW TO THE AREA. OUR FLT REQUIRED US TO LAND AT THE HELIPORT IN ZZZ; UNITED STATES. WE LANDED AND DROPPED OFF OUR PATIENT. OUR DEP PLAN WAS TO PROCEED VFR THROUGH CLASS B AIRSPACE TOWARDS XYZ ARPT. FROM XYZ WE WOULD PROCEED IFR TO OUR DEST. WE RECEIVED A CLRNC TO ENTER CLASS B AIRSPACE; AT WHICH TIME WE WERE INSTRUCTED TO CONTACT XYZ TWR FOR OUR IFR CLRNC. WE CONTACTED XYZ TWR AND DUE TO TFC WE WERE INSTRUCTED TO FLY TOWARD THE ARPT. AFTER SEVERAL MINS XYZ TWR CALLED US BACK WITH OUR CLRNC. I RECEIVED THE CLRNC AND WAS INSTRUCTED BY TWR TO STAND BY FOR THE READBACK. THE RTE POS PORTION OF THE CLRNC WAS DIFFERENT THAN WHAT HAD BEEN FILED. I ASKED FOR CLARIFICATION ON THE ROUTING AND IN ADDITION REQUESTED TO AMEND OUR FILED ALT TO 4000 FT VICE 6000 FT. OUR COMS WERE INTERRUPTED BY OTHER AIR TFC. WHILE THIS WAS HAPPENING I WAS LOOKING UP THE SID WE WERE GIVEN IN THE RTE CLRNC. OUR ACFT WAS APCHING THE ARPT AT 1400 FT WHEN TWR TOLD US TO FLY OVER RWY 24 AND TO PROCEED ON THAT HDG. THE TWR CLARIFIED THE PORTIONS OF OUR ROUTING THAT I HAD QUESTIONED AND TOLD US TO MAINTAIN 4000 FT AND TO EXPECT 6000 FT 10 MINS AFTER DEP. WE WERE TOLD TO MAKE OUR ALT CHANGE REQUEST WITH THE NEXT CTLR. I ACKNOWLEDGED THIS XMISSION ALONG WITH THE INSTRUCTION TO CONTACT DEP CTL. DUE TO THE NATURE OF THE COM INTERRUPTIONS; FLYING IN AN UNFAMILIAR AREA; WE BOTH THOUGHT THE SID PORTION OF OUR ROUTING HAD BEEN AMENDED BY VIRTUE OF THE HDG ASSIGNMENT AND ALT REFS. WE INITIATED THE CLB TO 4000 FT AND CONTACTED DEP CTL. UPON OUR INITIAL CONTACT WE WERE QUESTIONED AS TO OUR ALT AND INFORMED THAT WE HAD CLBED INTO THE APCH CORRIDOR FOR XYY ARPT. WE WERE GIVEN AN ALT AND VECTOR TO FLY. THE REMAINDER OF THE FLT WAS ROUTINE. RECEIVING AND CLARIFYING AN IFR CLRNC WHILE INFLT IN A HIGH DENSITY TFC AREA WAS PROBABLY THE MAJOR FACTOR IN THIS SIT. HAVING NOT ACCEPTED THE SID PORTION OF THE CLRNC AND INSTEAD REQUESTED ALT AND HDG ASSIGNMENTS WOULD HAVE MINIMIZED THE MISUNDERSTANDING BTWN TWR INSTRUCTIONS VERSUS SID PROCS.